Flying the Geology of the Island of Hawai'i: Part II - From the Waimea Plains to the Humu'ula Saddle

E mālama i ka 'āina, a mālama ka 'āina ia 'oe.

"Care for the land, and the land will care for you."
Hawaiian saying (source unknown)

Against a backdrop of Kohala's southwest flank, a helicopter emerges through the haze of grayish volcanic gas that wafted 60 miles from Kilauea volcano on the Big Island of Hawai'i. Brownish grasses on this arid side of the island are ineffective in concealing undulating waves of lava of the Laupahoehoe volcanics that flowed 20 miles from Mauna Kea volcano 4 to 7 ka. We're in the Waimea uplands, the plateau between rugged Kohala Mountain and the northern slopes of Mauna Kea. 

Kohala's last eruption was 120 ka in the late Pleistocene and has since been ravaged by erosion, diminished by subsidence and dissected by landslides that slid far out to sea. It's classified as extinct with little chance of re-eruption, although rejuvenation has occurred on other Hawaiian Islands. Over a thousand flows of lava for nearly a million years conspired to build Kohala and, along with flows from four other shield volcanoes, constructed the Big Island from the depths of the Pacific seafloor.

Through seemingly omnipresent volcanogenic haze, our helicopter wends its way across the Waimea Plain back to the heli-pad.

ALOHA!
This is my second post of four on "Flying the Geology of the island of Hawai'i." In Part I (here), following a review of two genesis theories of the Hawaiian Island chain, I discussed the volcanic landscape as my passenger jet descended on the Big Island. In this post and the two that follow, I took to the air on a 175 mile counter-clockwise loop of the island by helicopter. I've added some ground-based photos where contributory.

Yours truly with one of Sunshine Helicopter's Black Beauties

A STATE OF SUPERLATIVES
Hawai'i is the only state that is subjected to earthquakes, tsunamis, hurricanes and volcanoes. It's also known for its tremendous biodiversity with over 150 kinds of natural communities. In fact, seven ecological life zones exist from the sea to the summits that are a function of the variety of landforms, elevations and climate.

The "Big" island is the namesake of the Hawaiian Island chain and of course the state. It's not only the largest of the eight major islands in the Hawaiian archipelago (all the others fit into it), but it's the southernmost Hawaiian island and of the fifty states, the youngest island geologically and the only one that is volcanically active.

Almost 1,900 miles from the nearest continent (and 2,479 miles from L.A.!), the 1,600 mile-long archipelago stands isolated within the Pacific tectonic plate (a relationship that has puzzled geologists for over a century) and spans the north Pacific Ocean basin to the Aleutian arc in the north (beneath which it's subducting) with its continuation as the Emperor Seamounts. All combined, it's the world's longest chain of some 137 subaerial (above the sea) island volcanoes, islets, coral atolls and volcanic seamounts (submarine). If the Emperor-Hawaiian chain was arranged linearly (it has a dogleg in the middle), it would stretch across the Atlantic Ocean from Boston to Rome, Italy! 

The principal Hawaiian Island chain of eight major islands makes up 99% of the land mass of the archipelago. The remaining 1% exists as small volcanic and carbonate islands. Progressing northwest, they become increasingly smaller, eroded and subsided to the point of submersion, a relationship tied to their genesis.
Modified from Wikipedia

FOUR BLOG POSTS ON THE BIG ISLAND
The following image shows the arrival path of my passenger jet and subsequent helicopter flight around the Big Island. They are the subject of four posts, this being the second.

• Post I reviews Hawaiian geography and includes two antithetical hypotheses regarding the island chain's evolution. The post ends with my touchdown on the Big Island.
• Post II contains a description of the "life stages" of Hawaiian volcanoes and is followed by a helicopter geo-tour of the Big Island from the Waimea Plain through the lofty Humu'ula Saddle between volcanoes Mauna Kea and Mauna Loa. 
• Part III continues my heli-flight over active Kilauea caldera and then follows the East Rift Zone to the populated east coast town of Hilo.
• Part IV heads north along the east coast's sea cliffs to the Hamakua Coast, over the dramatic gorges of the Kohala Mountains and finally back to the heli-pad at Waimea.

 The Big Island of Hawai'i with its five volcanoes are depicted with vertically-exaggerated relief. 
Roman numerals indicate my flight path on each post beginning with my arrival (I). 
Computer-rendered Truflite image generated by Martin Adamiker of Wikimedia Commons

THE BIG ISLAND'S VOLCANOES
The Big Island consists of five subaerial volcanoes: Kohala (northernmost, oldest, extinct, most eroded and subsided; Mauna Kea (tallest and dormant); Hualalai (smallest and active on the west coast); Mauna Loa (active and largest on the planet); and Kilauea (currently active and youngest). The latter three are among the most active volcanoes in the world, having erupted within the last 200 years. 

Two volcanoes are submerged, one old and extinct and the other new and active. The sixth is Māhukona, an extinct seamount lying offshore northwest of the island that preceded the eruptions on the mainland. The seventh is Lō‘ihi, the newest submarine seamount in the Hawaiian chain, and will possibly emerge and fuse with the main island. It's active 980 m beneath the sea some 35 miles off the southeast coast of the island. The Big Island's volcanoes reflect a northwest to southeast progression of volcanic activity and geomorphology seen in the entire Hawaiian Island chain. It's a vexing geological relationship that's far from being completely understood. Please see my post Part I for details (here). 

THE "RAIN SHADOW" EFFECT
My aerial geo-tour began from Sunshine Helicopter's Hapuna Heliport (red dot below), a few kilometers above the Kohala Coast on the northwest side of the island. We're on the dry rainshadow or leeward aspect of Kohala volcano. Aridity is reflected in the scrubby, brownish vegetation, the paucity of streams that reach the coast and subdued erosion on the landscape. Visible from space, Kohala's east coast is heavily dissected into lush rainforest-blanketed gorges that open to the sea. We'll fly into them on our return flight in Post IV.

The northern peninsula of the Big Island is typified by Kohala volcano. The rainshadow effect on vegetation and the landscape is dramatic. The dotted arrow indicates the direction of my flight path from the Kohala Coast southeast toward the saddle between Mauna Kea and Mauna Loa.
Modified from Landsat 7 Satellite Image of Hunter Allen from USGS

The volcanoes of the Hawaiian chain block moisture-carrying, northwest trade winds from reaching the downwind sides of the islands. Moisture condenses as warm Pacific air rises and humidity increases. On leeward slopes of volcanoes, as moisture-depleted, cool air descends, it warms as relative humidity decreases. 

 From NOAA Climate.gov

The effect is most pronounced on the island of Hawai'i with the tallest volcanoes, but it can be observed throughout the island chain. Since they are the oldest, the islands of Kaua'i and Ni'ihau at the archipelago's northern end possess the most eroded volcanoes, the most soils and the most verdant vegetation since it has the smallest, moisture-blocking volcanoes. Notice the profound moisture-plume downwind of the Big Island. 

Seen from NASA's Landsat satellite, the wet and dry sides of the islands are juxtaposed in sharp contrast. 
Note the direction of the prevailing trade winds. The red arrow indicates the location of the heli-pad on the island of Hawai'i. Note the moisture-plume downwind of the Big Island.
Modified from NASA Landsat satellite photo

KOHALA VOLCANO
The view from Sunshine Helicopter's heli-port through the haze reveals five or six eroded cinder cones that erupted from vents along Kohala's Southeast Rift Zone. On Kohala's north side, another linear cluster lies along the Northwest Rift Zone. Forming the island's northern peninsula, it juts 20 miles into the Maui Channel (see map below). Rift zones usually appear as two elongate ridges or radiating fractures that transect the broadly sloping flanks of shield volcanoes. Fed from a magma chamber, it's easier for "fluid" basaltic lava to erupt laterally from the growing volcanic edifice than vertically through a tall central conduit to the summit, although both occur.

In addition to cinder cones, rift zones are the sites of spatter cones (lava blobs), pit craters (collapse structures along rift zones), faulting and open fissures on the surface. Kohala's Southeast Rift Zone is partially buried beneath hummocky lavas of later-erupting Mauna Kea that originated from the distant volcano. Typically, the Big Island's volcanoes, being massive and shield-shaped, coalesce at their bases with overlapping flows of lava. Their gentle slopes and large diameters are primarily a result of their composition of low-viscosity (low resistance to flow), mafic (dark-colored, mainly ferromagnesian minerals such as pyroxene and olivine) lava with relatively little tephra (ejected material).

An incoming Black Beauty glides into Sunshine Helicopter's heliport, which is built on flows from Mauna Kea that head downslope (left). Kohala's flank and cinder cones in the background consist of older Hawi Volcanics from Kohala that flowed almost directly toward the viewer.

A PERFECTLY PLUMACEOUS POSTULATION
Ancient Hawaiians recognized that the island chain possessed a northwest-southeast alignment, evidenced by their songs and chants. Their oral traditions conveyed they knew the islands were progressively younger moving down the chain. The observation was made by America's first volcanologist, James Dwight Dana, in the first scientific writings about the islands in 1849. But, it was independent workers - Canadian and American geophysicists J. Tuzo Wilson in 1963 and W. Jason Morgan in 1971 - that proposed fixed hotspots fed by a deep mantle plume for the genesis of the Hawaiian Islands. 

J. Tuzo Wilson, architect of the Hotspot hypothesis, and W. Jason Morgan, of the Plume Hypothesis.
Photos from Wikipedia and princeton.edu

The combined Hotspot-Plume hypothesis accounts for the Hawaiian Island chain's Pacific intraplate location and age-progressive volcanism with increasing distance from the hotspot. It is thought to be currently within the mantle beneath the Big Island's two active volcanoes (Mauna Loa and Kilauea) and/or under an active submarine volcano (Lo'ihi seamount). As oceanic lithosphere of the Pacific plate drifts across the hotspot, a linear progression of volcanoes is generated on the surface. Not only does the entire Hawaiian Island chain demonstrate a southward-trending age-progression, but the five volcanoes on the Big Island do as well, beginning with Kohala, oldest in the north, to Kilauea, youngest in the south. Our chopper flew through the age progression on the Big Island.

Diagram demonstrating the tectonic migration of the Earth's crust over the Hawaiian hotspot fed by a plume.
Modified from Wikipedia

Wilson and Morgan envisioned the global relevance to both continental and oceanic circumstances, the Hawaiian Islands is the type locality for the theory. Their explanation for the geological phenomena is the most popular but not the only one (again see Part I here).

THE "WONDERFUL LIFE" OF A HAWAIIAN SHIELD VOLCANO
The global system for classifying magma-generating volcanoes uses frequency of eruption: active (erupting recently or currently), dormant (not erupting for 10,000 years) and extinct (ceased erupting or unlikely to). A more descriptive, four-stage classification for Hawaiian shield volcanoes, proposed by Clague et al, takes into account their evolution through well-defined stages that are distinguishable temporally, geochemically, behaviorally, volumetrically and structurally. 

A Hawaiian volcano may not exhibit every stage, and the transitions may be gradual or rapid and may even involve substantial time gaps. Once manifested, they vary little and have implications to the stability and long-life of the hotspot. The following is a synopsis of the classic life stages expanded to incorporate post-eruptive processes:

1.)  Pre-Shield "youthful" Stage - The seamount (submarine volcano) or alkalic basalt stage lasts about 100,000 years with infrequent low-volumes but increasing eruptions of "pillow" basalts (enhanced Na and K possibly due to less partial melting around hot spot margins). Slopes are steep (10-15°) and unstable with a repetitively infilling caldera. Example: Lo'ihi Seamount (in transition to the Shield stage).

Submarine Pre-Shield Stage
Modified from Caden on Pinterest

Pillow basalts lying on the seafloor are formed by rapid cooling of quenched lava, a sure sign of submarine eruption.
From Wikimedia Commons

2.)  Shield "mature" Stage - Characterized by rapid and voluminous growth, 95-98% of the shield is built during three substages (submarine, explosive and subaerial) lasting perhaps 500,000 years. Alkalic lava transitions to tholeitic over the hotspot. Initial explosive sea eruptions form hyaloclastite pyroclastics (black sand) over pillow basalts from a shallow (3-7 km) magma chamber that generates voluminous subaerial flows of lava with greatest degree of mantle melting. The shield develops elongate subaerial slopes (5-8°) that feed eruptions via linear radiating rift zones. A large summit caldera forms with frequent slope landslides. Gravitational failure of unsupported, seaward-facing flanks exhibits submarine landslides across the seafloor. The volcano reaches maximum elevation during late Shield and early Post-Shield stages. 
Examples: Mauna Loa and Kilauea.
3.)  Post-Shield "old" Stage - The declining stage of ~250,000 years transitions back to more viscous and explosive alkalic basalt (hawaiite, mugearite and trachyte), while moving off the hotspot with diminished magma supply. As the magma chamber cools, volcanism fades and cinder cones form, indicative of a plumbing system change from the central conduit to rift zone fissure eruptions. Degradation exceeds aggradation as erosion produces gullies, soils and coastal features. Lavas contribute 1% of volcanic mass, eventually ceasing as the magma chamber cools and crystallizes. The composition of ultramafic and mafic xenoliths (non-magma-derived foreign-rock from the encompassing rock) provides clues to the depth and state of the magma chamber, and volcanic and mantle processes. 
Examples: Mauna Kea, Hualalai and Kohala.
4.)  Erosional Stage - The dormant stage of erosion as gravitational subsidence allows the development of coral reefs. 
Examples: Kohala and Northern Hawaiian Islands.

Subaerial Shield, Post-Shield edifice-building Stages and Erosional-Subsidence Stage
Modified from Caden on Pinterest

5.)  Rejuvenation Stage - Activity may resume following a <1.2 Ma hiatus with alkalic basalts and basanites (silica-depleted). Erosion continues with small volume eruptions possibly related to a nearby active volcano or remelting from depressurization of the eroding edifice. No volcanoes of the island of Hawai'i have reached this stage.
Example: On the island of Maui.
6.)  Coral Atoll, Seamount and Guyot Stage - The aged, extinct volcano has become a submerged seamount with a ring of coral atolls and finally a guyot (flat-topped seamount) with dead corals in colder waters. 
Examples: Northern Hawaiian chain and Emperor Seamounts.

Rejuvenation Stage, submarine Coral Atoll and Guyot/Seamount Stages
Modified from Caden on Pinterest

In summary, the eruptive life of a shield volcano can encompass 600,000 to a million years. Following a Pre-Shield Stage of slow growth with alkalic basalt (enhanced levels of Na and K), the volcano enters a long Shield-Stage of rapid growth with tholeiitic basalt that is followed by a Post-Shield Stage of reduced growth that transitions back to alkalic basalt. The chemical distinctions of basalt are thought to be related to the volcano as it approaches and departs from the hotspot. Older stages are demonstrated along the island chain AND on the Big Island from north to south, which has only younger, Pre-Shield through Erosional Stages.  

TEXAS TURKEYS IN TROPICAL PARADISE
While our pilot was conducting his pre-flight check, I was entertained by a most determined male turkey strutting around the heli-pad, displaying his plumage to a totally disinterested female who was more concerned with her next meal. Surprisingly, Hawai'i is a little known, tropical turkey paradise, popular among hunters. 

There's a large population on many of the islands, but they're non-indigenous to Hawai'i like so many of the flora and fauna. As early as 1788, they were reputedly descendants of free ranging domestic stock imported from Chile. In 1961, 400 wild Texas Rio Grande's were released at Pu'u Wa'awa'a Ranch on the Big Island. Some 16,000 feral turkeys now thrive on the islands of Hawai'i, Molokai and Lanai. There's more that meets the eye than courtship behavior!

An intent male Texas Rio Grande turkey and a highly indifferent female. Mating biology ultimately prevails.

Whether having arrived intentionally or accidentally (such as on early European and American sailing vessels), the subject of invasivity strikes at the heart of Hawaii's ongoing dilemma of protecting its evolutionary uniqueness and halting its declining biodiversity. When westerners first arrived, there were an estimated 70 native bird species. Today, 24 are extinct, and another 36 are endangered. How did this happen?

Hawai'i's isolation in the mid-Pacific Ocean has been conducive to the evolution of a vast array of plants and animals. Introduced naturally by insects and birds, it's estimated that only one plant every 90,000 years was added to the landscape, an astounding 90% of which exist nowhere else on the planet. Yet, non-native species such as the turkeys, of which there are many (here), have disrupted the natural balance that exists by over-competition or direct action. A classic Hawaiian example are rats and mongeese (plural?) that arrived in the last 200 years. The diurnal latter was introduced to exterminate the nocturnal, ship stowaway-former. Never the twain shall meet, while both eat native bird and turtle eggs.


GENTLY FLOATING ABOVE THE GRASSLANDS OF WAIMEA
Effortlessly, we lifted off from the heli-pad and began to cruise over the Waimea uplands (below) at about 1,500 feet, our altitude for most of the flight. A veil of atmospheric haze and blanket of vegetation fails to conceal the hummocky, overlapping flows of lava that solidified en route to the sea. 

Late in the Pleistocene, these lavas were buried by varying thicknesses of fine volcanic ash distributed by the wind. It formed the light brown to brownish-red Pahala Ash (as much as 55 feet thick near the town of Pahala south of Mauna Loa and 20 feet thick at Hilo). It chemically weathers to form the soils that support the grasses on which thousands of cattle once grazed in the uplands. They descended from five or so head that Captain George Vancouver brought over from England in 1793. The story is integral to the Big Island's fascinating history. 

Frozen in time, lava from Mauna Kea retains the surficial appearance when it was molten with the exception of a grassy cover and a network of streambeds pointing seaward.

Vancouver presented the cattle to King Kamehamela I, who ruled the eight Hawaiian Islands as one kingdom. The King allowed his cows to roam free, and it was, by his decree kapu, forbidden to kill them. In some 20 years, the cows exploded into a huge free-roaming herd that dominated the island by wreaking havoc on family farms and gardens. That proved extremely good fortune for a Massachusetts sailor named John Palmer Parker (from my hometown of Newton), who jumped ship in 1809 at the age of 19.

An elderly John Palmer Parker and portrait of King Kamehameha I
From Wikipedia

Parker tended the King's fish ponds for a while, departed for the War of 1812 and finally returned only with an American musket. The King allowed Parker to not only shoot the feral cows but supply meet and hides for local and foreign consumption. In less than a year, a thriving salt beef industry became a favorite provision on whaling ships and for native Hawaiians. It even replaced sandalwood, used in incense and for medicinal and ceremonial purposes, as the Island's chief export to China. They referred to the Hawaii as the "Sandalwood Islands."

Learning to speak Hawaiian and adopting their ways, Parker became a respected man of considerable wealth and influence. He married Kipikane, granddaughter of King Kamehameha I, and was awarded two acres of land on the slopes of Mauna Kea where they built homestead “Mana Hale” and started a family. At 500,000 acres, the ranch became one of the largest and most historic in the United States and was known for its Hawaiian paniolo cowboys. It was the beginning of the thirteen-generation Parker dynasty that played a prominent role in the next two centuries of Hawaiian history. 

In the Waimea uplands with a small cinder cone, the Parker Ranch headquarters as it looks today against a backdrop of snow-capped Mauna Kea

Greatly reduced in size today, yet the second largest landowner in Hawai'i, Parker Ranch is in trust and open to the public for touring and hunting. It includes 130,000 acres of working ranch and grazing land for 26,000 head of cattle and 300 breeding bulls. John's famous musket remains on display above the mantle in the Waimea main house.

KOHALA AND KONA WEST COASTS
From the uplands, we're looking down the south stretch of the island's west coast. Lava has flowed here from every volcano with the exception of Kilauea. Below the high clouds to the left and in the haze lies the edifice of 8,271 foot-high Hualalai volcano. On a clear day, we'd see the Kona Coast beyond Kona Airport. The green patch along the Kohala Coast to the right is a dozen luxury resort hotels and golf courses that were bulldozed out of thick flows of lava. Richard Smart, a successful theater entertainer and the Parker family's last descendant and sole heir to the estate, leased the land to the hotels back in the 1950's for financial reasons. Once again, this is the dry, sunny side of the island.

Semi-obstructed by volcanic haze from Kilauea and ever-migrating reflections on the helicopter's cockpit, we cruised over Waimea grasslands veneered by lava flows from Kohala, Mauna Kea, Mauna Loa and Hualalai (progressing southward) that drape seaward toward the Kohala and Kona coastline in the distance.

HUALALAI VOLCANO
Hualalai is the third youngest volcano on the island and has been in the Post-Shield stage for 100,000 years. Its most recent eruptions came from the Northwest Rift Zone in 1800 and 1801 and produced the Ka`upulehu and Hu`ehu`e flows, respectively. The latter forms a platform on which the airport is built. By definition, that makes Hualalai active and likely to erupt in the next century or two. In fact, 80% of its surface has been topped by lava flows in the last 5,000 years and poses a great potential threat to thousands of people that live along the coast.

This three-photo panorama of Hualalai, 20 miles to the south, is taken while standing on a barren, dark, recent lava flow from Mauna Kea (off to the left) that traveled 40 miles to the Kohala Coast. Typically, clouds are developing on its east flank (left) with none on the west (right). The 'bumpy' profile of cinder cones along the Northwest Rift Zone is typical of the volcano's Post-Shield Stage. Prominent Pu'u Wa'awa'a cinder cone (arrow) is discussed below.

Photographed on the Kohala Coast from within a historical (1859) unvegetated, twenty foot-thick fortress of lava that flowed over 40 miles from vents on Mauna Kea, distant Hualalai is peppered with over 120 cinder cones that are aligned along two rift zones. This is typical of late-stage, declining volcanic activity. Additional signs of magmatic activity include an intense earthquake swarm in 1929 that originated from its summit. 

View of the cinder cone-peppered summit of Hualalai from within a Mauna Kea ʻaʻā lava flow 
that traveled some 40 miles across the landscape to the coast.

PU'U WA'AWA'A HELPS CLARIFY A FEW ENIGMAS
North northeast on Hualalai's base and six miles from the summit, cinder cone Pu'u Wa'awa'a erupted about 105,000 years ago. It's the oldest surface feature on Hualalai and is surrounded by relatively recent flows. Geochemically, it's unlike the other cinder cones on Hualalai's flanks and reflects a transition back to alkalic basalt. It stands 1,220 feet and is over a mile in diameter. Scored by radial ravines, which explains its Hawaiian name "many-furrowed hill", the cinder cone is of great geological importance. 
  

Pu'u Wa'awa'a is a trachyte cinder cone located at the base of parent Hualalai volcano (to the right).
It has a unique geological, biological and archaeological history.

Mound-shaped Pu'u Wa'awa'a erupted from the Northwest Rift Zone and is constructed of trachyte pumice - a high-silica, steep slope-producing, viscous lava. Trachyte is a thousand fold increase in viscosity over that of more "runny" basalt. It's also rich in sodium and potassium, molecularly-large elements that impede flow, which explains the cone's domal massivity and steep flanks. Downslope from Pu'u Wa'awa'a extends the Pu'u Anahulu trachyte Ridge (Google Earth image below).

In this southeast-facing, Google Earth view (2x vertical exaggeration) of the Big Island of Hawai'i are the shield volcanoes of Mauna Loa and Hualalai. Hualalai's Northwest Rift Zone posseses aligned cinder cones with Pu'u Wa'awa'a trachyte cinder cone and Pu'u Anahulu ridge off to the north northeast. Notice the lava flows from Mauna Kea and Mauna Loa that made it to the Kohala Coast near the hotels, where the two photos of Hualalai were taken.

A PETROLOGICAL BAROMETER OF MAGMA DIFFERENTIATION
The igneous rock trachyte exists on no other Hawaiian Island. It's well-differentiated or "highly evolved", meaning an end member in the alkalic basalt series. To explain, igneous rocks commonly show a bimodal distribution, one being basalt and the other, felsic magmas. As fractional crystallization (chemical evolution) of basaltic parents produces a continuum of compositions, the paucity of rocks of intermediate composition - called the "Daly Gap" - puzzled petrologists since Reginald Daly first observed the phenomenon in 1925. The "magmatic gap" has numerous explanations, all of which hint at the petrological processes that occur within the mantle.

These magmas are associated with the Post-Shield alkalic Stage. One theory indicates a reduction in the supply of magma from the mantle or melting of sub-volcanic crust during the final stages of edifice construction. The Shield Stage, when the volcano is centered over the hotspot, occurs when tholeiitic magma is stored in a shallow reservoir some ~3-7 km of depth beneath the summit. As the volcano moves away from the hotspot (below), it enters the Post-Shield Stage with decreased mantle melting and magma supply, freezing of the reservoir and fractional crystallization of magma in deep reservoirs (~20 km). 

DALY'S MAGMATIC GAP FITS INTO THE VOLCANIC BIG PICTURE
Fractional crystallization occurs as magma cools and melts. Its blend of minerals form in a specific order becoming highly evolved. Thus, Pu'u Wa'awa'a's unique lava composition (see trachyte under 1% on the image below), which also includes xenoliths transported to the summit from Hualalai's central conduit. It serves as a "petrological geo-barameter" indicating not only the transition to the Post-Shield Stage but information about volcanic processes and late-stage magma evolution. It conveniently fits in with the Hotspot-Plume Hypothesis - the tectonic migration of the Pacific Plate over a hotspot anomaly.

Progression of magma generated from Hawaiian shield volcanoes as the Pacific plate migrates over the hotspot. The magma becomes alkalic at the beginning and end of volcano-building with distance from the hotspot. The magma is thought to remain within the crust longer which alters its composition.
Modified from luckysci.com and Clague, 1987

PU'U WA'AWA'A IS ALSO A BIOLOGICAL AND ARCHAEOLOGICAL TREASURE
Biologically, Pu'u Wa'awa'a is home to the Nene goose (the Hawaiian State bird), the ope'ape'a (the Hawaiian Hoary bat), the 'oka'i (the endangered Blackburn Sphinx moth), the yellow Hawaiian hibiscus (the State Flower) and a plethora of native plants, 40 of which are rare and 20 of which are endangered. 

The Nene (NAY-nay) is currently on the Federal List of Endangered Species. It has endured a long struggle against extinction from hunting during breeding season, predation by alien species such as mongoose, rats, and feral dogs and cats, and even frequent automobile strikes. An estimated 25,000 Nene were on the Big Island when British explorer Captain Cook landed in 1778, the first recorded European contact with the Hawaiian Islands. When Nene hunting was banned in 1907, around 30 were left. Today, conservation efforts have brought their numbers back to almost 1,000. This is a typical story of the struggle that ecologists and conservationists are engaged in on the Hawaiian Islands.

The Nene goose is the Hawaiian State bird with a characteristic deeply-furrowed neck.
Its lifespan may be 35 years or more.

Archaeologically, obsidian (a hard, dark, glass-like volcanic rock formed by rapid solidification of lava without crystallization) is found no where else in the Hawaiian Islands. It was a source of lithic tools for much of Hawaiian prehistory. Artifacts found at various sites have produced dates in the 17th to 18th centuries but was likely used far earlier.

A WORD OR TWO ABOUT HELICOPTER PHOTOGRAPHY ON THE BIG ISLAND
Aerial photography from a helicopter is a delight due to the low altitude, its hovering capability, reduced air speed, minimal vibration and ease of re-takes, but there are challenges. The haze on the island's western half affects clarity and contrast. You're inside a rotating fish bowl where even a small scratch or smudge on the glass becomes illuminated by the sun! You'll also have to contend with glare of the sun constantly migrating inside the canopy, the cockpit struts that block one's view and internal reflections of occupants on the glass. Photo tips: Wear black not white to reduce reflections, and use manual focus to prevent auto-focusing on the glass canopy. 

You can request a front seat and that the passenger door be left off, but you'll pay extra. Mornings and afternoons produce the best light, but the deep gorges won't be fully illuminated. They generally open to the east and face the morning sun. Fast shutter speeds will quell vibrations. Use a wide angle lens but not excessive or you'll catch the struts. Post-editing will help with the haze. Lastly, request speakable-headsets to allow communication with the pilot, otherwise you'll have to gesture photographic requests. 

Drifting internal reflections, glaring sun spots, canopy struts and volcanic vog can be challenging photographically. That's Mauna Kea with its cinder cones in profile.

BLOWIN' IN THE WIND
This sunny February morning, the haze seemed everywhere but was actually minimal according to the pilot. It's easily mistaken for low, thin clouds, but it's actually vog - a portmanteau of the words "volcanic", "smog" and "fog." It's a vaporous cocktail of 80% water vapor and lesser amounts of sulfur dioxide, carbon dioxide and hydrogen, and minute amounts (less than 1%) of carbon monoxide, hydrogen sulfide and hydrogen fluoride - all energized by the sun and all from Kilauea. 

Sulfur oxides in vog react with moisture and fine particulates to form an oxidized aerosol that scatters light. Carried by wind from fuming vents on distant Kilauea, it lingers between 300 and 6,000 feet but mainly 1,000 until dispersed. Kilauea emits 2,000 to 4,000 tons of sulfur dioxide every day! I found it ironic to leave mainland urban and industrial pollution, travel half-way across the Pacific Ocean and encounter smog, albeit in a natural form. Yet, man's contribution to a polluted atmosphere is small compared to volcanic emissions, which by the way are responsible for the generation of the Earth's early atmosphere through the process of outgassing. 

Although Kilauea (left) is a small to medium-sized volcano, it is the single dirtiest power plant on the planet, albeit natural. Of course, carbon dioxide emissions from human activity and the burning of fossil fuels have climbed at an ever-increasing rate and threaten to tip the scales.

This oblique, northerly view of the island of Hawai'i shows southwest-trailing plumes rising from Kilauea's summit crater (the thin plume) and cinder/spatter cone (lower to the right) on the East Rift Zone. In total, they create an ephemeral, low-lying blanket of vog that drifts over much of the island by the prevailing trade winds from the northeast. That's the island of Maui across the channel.

 From Wikimedia and the NASA Earth Observatory photographed by the NASA STS-125 crew of the Space Shuttle Atlantis, 2009

Vog acts as nuclei for condensation in the formation of clouds, which correlates with reduced rainfall. Being weakly acidic, vog enters the water supply and can damage crops. In sensitive individuals it can produce headaches, lethargy, allergy symptoms, and respiratory and eye irritations. In high concentrations, it's life-threatening in individuals with pre-existing medical conditions such as asthma and coronary artery disease. Should levels become high, health officials recommend leaving the area, minimizing physical activity, listening to civil defense updates and entering safe-rooms in homes and schools. 

Air quality warnings are ubiquitous in Hawai'i Volcanoes National Park.
This one is near Kilauea's fuming Sulfur Banks

LIVING ON THE EDGE IN PARADISE
Subject to the whim of the wind, vog can be problematic all across the Big Island and has even been detected on O'ahu, some 350 km northwest of Kilauea. Air quality is closely monitored and health alerts are posted to the website of the USGS's Hawaiian Volcano Observatory (here) and (here). There's even a downloadable app, but a low-tech way to assess air quality is to simply check the horizon for clarity. 

The emission of volcanic gases and steam is associated with active volcanism as are earthquakes, which may foretell the eruption of a volcano. It's all intensely monitored by the HVO. Seismologists estimate a 50% risk of a destructive magnitude 6.5 or higher quake striking the Hawaiian Islands in the next 10 years. The USGS also maintains a Volcano Hazards Program, rating system and website online (here).

 This is a sample air quality posting for 10/9/15. Due to emissions from the Kilauea volcano, the State of Hawaii Department of Health Short Term Sulfur Dioxide Advisory is posted online for the Big Island.

THE "WHITE MOUNTAIN"
Continuing on our flight to the south, we approached 13,796 foot-tall Mauna Kea. The volcano dominates the landscape of the northern third of the island. It's also the highest point in the state and tallest volcano on the planet. Measured from its oceanic base, it's taller than Everest (29,029 feet) at 33,000 feet. Mauna Kea is a million years old and is considered active, having erupted only 4,500 years ago. That places it within the Post-Shield Stage like abutting Hualalai and Mauna Kea. Typical of late stage activity, over 300 cinder cones and alkalic lava flows of the Laupāhoehoe formation adorn its slopes that have buried tholeitic basalts of the Hāmākua formation that built the bulk of the shield.   

With only patches and streaks of winter snow at the summit, Mauna Kea hosts thirteen astronomical observatories and many cinder cones both on its summit and flanks.

The summit is thought to have collapsed into a caldera and subsequently buried by cinder cones and tephra. Although classified as active, the risk of re-eruption is considered low enough for an investment of over a billion dollars in 13 international astronomical observatories on the summit. Arranged in a semi-circular array, their positions imply the partial outline of a caldera. Another observatory and a military operations area are planned, subject to the resolution of ongoing cultural, religious and environmental objections.

Summit view of Mauna Kea's observatories facing west. Click for a larger picture.
With permission from Jean-Charles Cuillandre, astronomer/photographer at Canada-France-Hawaii Telescope

HAWAIIAN FIRE AND ICE
In Hawaiian mythology, Poliʻahu is one of four goddesses of snow, all enemies of Pele, the Fire Goddess and creator of the Hawaiian Islands. Poliʻahu resides on Mauna Kea, the most sacred of the Hawaiian volcanic mountains, and threw snow at Pele's lava, freezing and confining it to Mauna Kea. Mythology and geology are in full accord!

Winter snows on Mauna Kea persist at upper elevations, which explains why Hawaiians call it the "White Mountain." Just think - seasonal tropical skiing without lift tickets! It's a reminder that four glacial episodes blanketed the upper reaches of the volcano during the Pleistocene over a span of some 300,000 years. It might seem contradictory that a tropical island within 20° of the equator could have experienced glaciation, but during the Pleistocene, Mauna Kea was high enough to sustain climatic glaciation that affected the entire planet. In fact, Mauna Loa may have had an ice cap as well. 

Artist's depiction of the Hawaiian Island chain with the glaciated summit of Mauna Kea on the Big Island
From dailygalaxy.com

Left: Map of Hawaii showing the five volcanoes that comprise the island (contour interval 103 m). The summits of Loihi and Mahukona volcanoes lie below sea level. Only Mauna Kea has a definitive 
stratigraphic record of glaciations, but Mauna Loa may have had an ice cap during the last glaciation. The extent of the last Makanaka ice cap is outlined on Mauna Kea (blue). Right: Map showing extent and surface topography of the Makanaka ice cap at the last glacial maximum about 20,000 years ago. Bold dashed line represents the reconstructed full glacial equilibrium line (EL) of the ice cap, and dotted lines show east-southeast-sloping gradient of the equilibrium-line altitude (ELA) surface across the glacier.
Modified from Stephen C. Porter, 2005

On Maui, the next island to the north, Haleakala volcano is thought to have stood higher than the last glacial maximum snowline of Mauna Kea (16 to 19 ka). Unsorted mudflows (with glassy margins and crystalline plagioclase that imply rapid quenching) and gravelly diamictons (unsorted to poorly sorted sediment from clay to boulders, whereas, tills are specific to glaciers) infer a history of glaciation. Mauna Kea has provided the only opportunity to study a record of actual glacial deposition in the tropical Pacific Ocean and is of broad significance in understanding the nature of global climate change.

There's no mistaking the classic shield shape of a Hawaiian volcano such as Mauna Kea, seen from the Mauna Loa Observatory at the summit. The light-colored upper reaches of the volcano consist of glacial till, and the down-pointing lobes and ravines were created during glaciation. Silent cinder cones are in profile.
Wikipedia by Nula666

The conditions under which a glacier forms requires surprisingly little change from Mauna Kea's present climate. It's estimated all that was required for glaciation in the Quaternary (the last 2.6 million years) was an additional two inches per year in rainfall and an average temperature reduction in only a few degrees. It's enough of a climate change that accumulation over time exceeds melt.

How does that occur? Hawaii's marine reef terraces, along with Barbados, New Guinea and Australia, provide convincing arguments in support of glaciation's association with astronomical parameters (Milankovitch theory), tectonics (movement of continents to higher latitudes, creation of orographic barriers such as mountains, and closure of the Isthmus of Panama), and subsequent changes in ocean circulation (such as the Gateway Hypothesis), which affect marine temperatures and salinity. 

TROPICAL ICE
Mauna Kea's ice cap is defined by its moraines that reached 10 km in diameter as of the last glacial maximum about 21,000 years ago with an area of 70 square kilometers and average thickness of 70 meters with thickest ice exceeding 100 km. Light-colored, lobate deposits that circumvent the summit (photo above) represent till (unsorted glacial sediment derived by erosion) down to 10,500 to 12,500 feet. 

As the ice age ended, glacial ice globally began to diminish, but Mauna Kea's glacier began to re-advance about 14,500 years ago. That coincided with a slowdown of the Atlantic Meridional Overturning Circulation (AMOC) in the North Atlantic Ocean, a portion of the global circulation system that carries heat from the tropic to the North Atlantic. It created a warmer Europe in the winter in the process and made it habitable for the development of European civilization. Getting back to Hawaii, Mauna Kea's data shows the AMOC's decline correlates to global climate changes.

Northeast view of the summit of Mauna Kea from the Saddle shows two ridge-like lateral moraines of the Makanaka and Waihu glaciations at the top of Pohakuloa Gulch, deposited over interstratified post-shield lavas. The width of view at the moraine belt is 2 km.
From Porter, 2005.

SIMULTANEOUS GLACIATION AND VOLCANISM
At various times during the Pleistocene, lava from Mauna Kea contacted glacial ice, certainly a most violent and spectacular event. Flows within the moraine belt contain features that confirm this such as abnormally high and steep lava margins, pillow basalt structures and hyaloclastites (found in submarine eruptions in early life stage from rapid cooling). The crests of several cinder cones projected above the glacial surface and are marked by hawaiite erratics on their flanks, a fine-grained olivine-rich basalt. 

Lava of hawaiite that chilled against the ice provided early Hawaiians with an excellent source for chipping stone tools such as an adz, an axe-like tool. Post-glacial, unglaciated 9,000 year-old cinder cones have been useful in dating Mauna Kea's eruption rate, thought to be about once every millenium. Some of these cinder cones are so glacially gouged and dissected that the internal vents that were active during their formation have been exposed.

On Mauna Kea's south flank at 11,000 feet and about 2,000 feet from the summit, unsorted glacial till litters the landscape. An excavated and glaciated cinder cone clearly has till distributed about its base. Notice also the Makanaka morraine from the penultimate Waihu glaciation extending off to the right. This photo was taken from the Summit Road on a Mauna Kea Expedition ground tour.

Pleistocene glaciers occupied Mauna Kea's summit about 70,000 years ago, 40,000 and lastly at 13,000. The average thickness is estimated at 260 to 560 feet. Evidence for glaciation includes till, moraines, glacial striae on lava flows, and roches moutonnees (a "sheep-rock" shaped, erosional rock formation). 

Photographed from a bouncing Mauna Kea Expedition van, we're facing south, downslope from Mauna Kea at about 10,000 feet. The Mauna Loa Observatory Road winds in and out of cinder cones on a landscape littered with glacial till that terminates just below the cones. Poking through the clouds induced by ascending trade winds (upper right) is the east slope of massive Mauna Loa.

Even from a distance, Mauna Kea can be seen covered by light-colored till that marks the extent of the ultimate Makanapa glacial episode, which covered some 27 sq.mi. Several glacially-eroded canyons, locally called gulches, radiate from the summit and coincide with the location of glacial lobes, the source of erosive meltwater. In particular, Pohakuloa Gulch reached 10,200 feet (below left). Glacial outwash consisting of finely-ground rock powder, which would expected to be at the mouth of the gulch, was buried beneath recent flows from Mauna Loa. One such flow is in the foreground very bottom of photo). If Mauna Loa was covered by glacial ice, the evidence appears to be erased or buried by recent eruptions. 

North facing view of Mauna Kea from the Saddle Road within the Humu'ula Saddle. On the south side of the road is Kipuka Pu'u Huluhulu. Notice the dark, unvegetated lava flow immediately in the foreground and the older vegetated flow upslope. Mauna Kea, in keeping with its post-shield stage, possess numerous cinder cones in the vicinity of a buried rift zone.

As sea levels fell globally during Pleistocene glaciation, the erosion of paleo-coastlines occurred. Today, with sea levels high, they occur as submarine, wave-cut platforms and benches in coral reefs at prior high-stands.  

Drowned intertidal notch on the Hawaiian Island of Molokai. Its depth coincides with the coral framework stratigraphic record. Much work has also been done on the Oahu shelf.
From Charles H. Fletcher et al (Geology of Hawaii Reefs, 2008)

SAVING AHINAHINA. SAVING HAWAII ON MAUNA KEA.
The geographical isolation of Hawai'i has strongly influenced its biodiversity. Typical of all the islands, Mauna Kea's ecology became severely damaged beginning in the late 18th century when European settlers introduced cattle, sheep and game animals, many of which have subsequently become feral. There are countless examples of alien species outcompeting and destroying indigenous flora and fauna. By 1851, there were an astounding 3,000 feral sheep and 12,000 feral cattle on Mauna Kea, and in the 1930's, the sheep exceeded 40,000. Their foraging activities decimated Mauna Kea's population of indigenous plants, in particular the Haleakalā silversword plant, which is a prime example of adaptive radiation and evolution under restrictive ecological conditions. 

The Haleakalā silversword has an array of sword-like succulent leaves covered with silver hairs. It grows well on volcanic cinder that is subject to freezing temperatures and high winds at high altitudes. The skin and hairs are strong enough to resist climate extremes and protect the plant from dehydration and the sun. It may slowly grow in excess of 50 years.

Ahinahina, the Hawaiian name, is a member of the daisy family. It's a federally-listed, highly endangered, strikingly beautiful, endemic flowering plant that thrives in a high, harsh, dry environment such as found on Mauna Kea's wind-swept desert of cinders. It was thought that the plant was restricted to the alpine zone but was actually driven there by excessive grazing, especially wild goats - non-indigenous of course! In addition, the plants were harvested for dried table arrangements. Being so slow-growing, their numbers have been drastically reduced.

Near extinction (in 2003 only 41 existed in the wild), extraordinary and successful conservation efforts to preserve the species are conducted at an elevation of 9,000 feet by cultivating them in fenced enclosures. Hand pollination is utilized, since invasive Argentine ants have interfered with native bee pollinators in what seems to be a repetitive theme in Hawai'i. There are currently over 8,000 surviving plants in the wild, cultivated from only six wild founders!

Gated, goat-proof enclosure at 9,000 feet on Mauna Kea for the cultivation of the silversword

Back to the flight!

FORMER PARKER PASTURELAND
We're still flying over former Parker pastureland as the landscape reflects the rising northwest flank of Mauna Kea. Quite unexpectedly, we crossed a remote 2,000-acre master-planned community called Waikii Ranch; otherwise, the flanks are unpopulated. A cluster of cinder cones are in profile with elongated flanks to the west that conform to the direction of the prevailing northeast "trades." In the background, Mauna Loa's eastern flank has an almost imperceptible slope. We're approaching the saddle, the high plateau region between the two volcanoes. Mauna Kea's basaltic shield is buried by the eruption of voluminous, late stage pyroclastic materal. It's the source of the soils that nurtured the grasses on which the King's cattle fed. 

PRECIOUS LANDS WITH INFERTILE SOILS
Chemically and physically weathered soils in this region of the island are created from the aforementioned volcanic ejecta (andisols from Pahala ashfall deposits) and basaltic lava (infertile oxisols). Closer to the coast, mollisols are dark-colored, often reddish, nutrient-rich, high-iron soils. These volcanically-derived soils support the grasses on which Parker cattle and sheep grazed. On the wet, east side of the island, where sugar cane historically was cultivated and other crops such as  grow today, soils are also derived from organic materials (such as histosols).

The rusty-reddish color of the soil is deceiving in that it is extremely infertile. Silicate minerals in the volcanic constituents turn into various clays, while most of the phosphate, magnesium, calcium, sodium and potassium enter into solution. Precipitation, especially on the wet side, leaves the residue a kaolite clay and converts the tropical soil into laterite. Devoid of soluble fertilize-minerals, it's infertile, although stained red or yellow by oxides of aluminum and iron. The island of Hawai'i, being the youngest in the chain, possesses the least soil diversity, mapped below. In spite of that, the plants of its rainforests are highly adapted to grow in the highly acidic, extremely infertile conditions. 

Soil Orders of Hawai'i
From Soils of Hawaii (Deenik and McClellan), 2007.

HUMU'ULA SADDLE
Geologically, Humu'ula Saddle is a high-altitude plateau of overlapping Mauna Kea and Loa lava flows and intercalated pyroclasts formed by the coalescence of the two volcanoes. Geographically, it's the unpopulated, minimally to unvegetated center of the island. Militarily, it's the largest Department of Defense training center in the Pacific. 

The bedrock map (below) of the Big Island's interior illustrates the merging of the two volcanoes at their bases in the saddle (ellipse) and recent lava flows of Mauna Loa that diverged either northwest or east to the coasts. An eastern flow almost devastated the coastal town of Hilo in 1855-1856. Since 1843, Mauna Loa has erupted 33 times from the summit and downflank from vents along its two rift zones. Flows from the Northeast Rift Zone remain a significant hazard to Hilo, which is exploited by lava flows that funnel towards Hilo within the swale between Mauna Loa and Kea created by the Wailuku River from the eastern slopes of Mauna Kea. Hilo, the unofficial tsunami capitol of the world, is also "exploited" by tsunamis and hurricanes that enter shallow, funnel-shaped Hilo Bay.

Surficial bedrock map of the central portion of the isalnd of Hawai'i. The flows that emanated from vents of Hualalai, Mauna Kea, Mauna Loa and Kilauea are easy to indentify. Click for a larger view.

The Big Island has been divided into nine lava-flow hazard zones, but essentially there's little that can be done when flows encroach populated areas. At best, they provide an indication of risky areas to live (or not to live). As recent as 1942, Mauna Loa sent lava flowing into the saddle that went east within 23 miles of the coastal town of Hilo. Dr. Thomas Jaggar, director of the Hawai'i Volcanoes Observatory, persuaded the U.S. Army Corps of Engineers to drop 500-pound bombs on the lava in a attempt to halt its advance. Their efforts were unsuccessful and likely aroused the wrath of Madame Pele, the Hawaiian fire goddess. A notable exception to flow attenuation is Vestmanneay, a fishing village on an island off the coast of Iceland, that was inundated with basaltic flows from Eldfell volcano in 1973 and successfully doused and halted with sea water.

HISTORICAL ERUPTIONS OF MAUNA LOA
Early Polynesian settlers certainly witnessed active eruptions from Mauna Loa, but preserved no recorded accounts. The first written account was by a missionary who documented a June 1832 eruption from Maui, the next Hawaiian Island to the north. In 1882, American missionary and minister Titus Croan published an extensive 23 chapter book entitled "Life In Hawaii", which is available online by his son since 1997 (here). Croan met the preeminent American geologist and volcanologist James Dwight Dana, whom he corresponded with for four decades. His accounts were instrumental in assisting Dana in formulating his theory on the evolution of the Hawaiian Islands. 

Here's an example of his firsthand colorful and descriptive text:

"The great eruption of 1855-56 continued fifteen months and the disgorgement of lava exceeded by millions of tons that of any other eruption we have seen. It was first observed on the evening of the 11th of August, 1855, shining like Sirius at a small point near the summit of Mauna Loa. This radiant point expanded rapidly, and in a short time the glow was like that of the rising sun. Soon a deluge of liquid fire rushed down the mountain-side in the direction of our town (Hilo)." 

From Life In Hawaii by Titus Coan, 1882, Chapter XXI - The Eruption of 1855

CINDER CONES GALORE
As we climbed higher into the saddle, a field of cinder cones from Mauna Kea came into view, formed during the Post-Shield Stage in the Pleistocene. They varied in architecture 
from pristine and angular to eroded and diminutive. Mauna Kea's rift zones are less pronounced than on neighboring volcanoes, which results in a more scattered cinder cone distribution within the saddle, although some do exhibit some degree of alignment. 

Massive Mauna Loa with a snow-speckled summit looms large. Its flanks (as is the entire island) are composed of an intermingled patchwork of old and new flows. They are distinguishable by their color and degree of vegetation. New flows are darker, unoxidized and devoid of soils necessary for plant growth.

 Having entered the saddle, that's Mauna Loa in the distance.

Appearing like eroded, breached cinder cones, the occasional rises on the landscape are tumuli. Typical of basaltic lava fields, they form from the injection of very fluid lava beneath a still hot, deformable plastic crust. Many of these features partially collapse or deflate after their margins have solidified and form a central depression surrounded by a ridge that is steep-sided towards the volcano with the depression open downslope. The direction of the sea is obvious from the dip of the slope, strike of the flows and the direction of streams that have begun to dissect the landscape.

A tumulus on flows that originated from Mauna Kea

From above, concentric, overlapping pahoehoe (pah HOY HOY) lava appears like layers of an onion. Two types of lava emanate from Hawai'i's shield volcanoes. Both are basaltic in composition and chemically indistinguishable. Their low viscosity (relative fluidity) and flow characteristics are related to chemical and gas composition and temperature (please see Part I for details here).

Swirling concentric pahoehoe lava flows

Pahoehoe (pah HOY HOY), possibly from the Hawaiian word for "paddles" that cause water to swirl, forms in smooth, shiny, undulating ropy bands that form often when the effusion rate is low. With a temperature of 1,100 to 1,200°C (2,010 to 2,190 °F), it advances by the propagation of lobes and feeds well-insulated, subsurface tube systems. 

Shiny, smooth and ropy pahoehoe lava flow from Mauna Loa the emplaced during the 19th and 20th centuries along Saddle Road. Mauna Loa in the haze looms large in the background.

ʻAʻā (AH ah) lava, from the Hawaiian name for the brightest star Sirius (although many suspect it's for the pain experienced when walking on it) has a blocky, rough, clinkery, jagged and spiny surface. Erupting at 1,000 to 1,100°C (1,830 to 2,010 °F), it advances by widespread fracturing of the exterior of the flow and moves as a single unit. ʻAʻā flows tend to be thicker (2-10 m) than pahoehoe (0.2 to 2 m) and of higher viscosity with a higher volume flow rate and higher flow-front velocity.

Ropy and blocky juxtaposed, a recent ʻaʻā flow overlaps one of pahoepahoe along the Crater of the Moon Road south of Kilauea.

Higher in the saddle, this shrub-covered cinder cone has a road that spirals to its well defined, truncated (cut off) summit and funnel-shaped crater. Composed of gas-filled, "cinder-like" scoria, when molten basaltic lava emerges under pressure from a vent, cinder cones are frequently steep due to a high angle of repose, up to 30 as opposed to "parent" shield volcanoes with a slope of 5-7. In contrast, light-colored grayish pumice forms from rhyolitic magmas, which usually contain more gas. Its base has been mined for likely for light weight aggregate or use in construction cements. 

For the record, basaltic cinder cones also appear on monogenetic volcanic fields (see here) and on the flanks of steep composite (strato-) volcanoes (of felsic and intermediate igneous rocks) via the accumulation of basaltic bombs, blocks, rock fragments and scoria. There, lava frequently exudes down the landscape from a flanking breach (and here). 

"LONG MOUNTAIN"

Patches of remnant winter ice are visible on Mauna Loa's summit at 13,678 feet above sea level. Its low profile slope belies the volcano's enormous masssivity, which has depressed the seafloor making it 56,000 feet tall. Compared with Mount Shasta's volume of 80 cubic miles, the second highest peak in the Cascades of California, Mauna Loa has 18,000 cubic miles. Hawaiian for "Long Mountain", measured from its submarine base (~4,200 m below sea level), it's the both the largest and tallest mountain and volcano on the planet. These numbers don't convey Mauna Loa's true height, since the oceanic lithosphere on which it rests is isostatically depressed an additional 8,000 m. Thus, its "true" corrected height exceeds 17,000 m - double that of Everest, which is above sea level! On the surface, it covers over half the Big Island. 

If the early Hawaiians that called Mauna Loa the "Long Mountain" knew of its actual height measured from the ocean floor, they might have used a more superlative adjective to describe it. Compare its massivity to Mt. St. Helens that rests on continental lithosphere.
From opentectbc.ca

Having erupted 39 times since its first historical eruption in 1832, it's considered active, near the end of the Shield Stage, but in a state of slow demise, as evidenced by the initiation of a transition to alkalic lavas (from radial vents other than the summit and rift zones) and the anticipation of of a decrease in the rate of eruptions. In 1984, lava erupted along the Northeast Zone and came within four miles of Hilo. It erupts less frequently than neighboring Kilauea but produces a greater volume of lava over shorter period of time. 

With massive, ice-capped Mauna Loa dominating the landscape, the Saddle Road (Route 200) rises within the the lofty intermontane plateau between volcanoes Mauna Loa and Kea. A maze of barren, dark new flows heading northwest are easy to distinguish from older vegetated ones, some of which have reached 40 miles to both the east and west coast.

Mauna Loa has two rift zones from which its lava flows have emanated, a short Northeast Zone terminating at Kilauea and a long Southwest Zone that enters the ocean at the island's southernmost South Point. Summit crater Moku`aweoweo, named after a red Hawaiian fish, is comprised of three overlapping pit craters. 

From hvo.wr.usgs.gov

SLUMPS, LANDSLIDES, FAULTS AND ESCARPMENTS
Mauna Loa's west flank has been the site of extensive slope failure in the form of slumps (slides) and gravity-driven debris avalanches (volcanic landslides). Often demarcated by pali (headwall cliffs), the former can be 25 miles wide and six miles deep and can occur abruptly or gradually over time and extend offshore to great depths. A massive, down-dropped block lies between the seaward-facing faults of Kealalekua on Mauna Loa's west flank and Kahuku striking south that continues undersea. The latter fault defines the Kahuku Pali escarpment (far left below) at South Point that is shrouded in Kilauean vog. 

The most destructive earthquake in Hawaiian history, related to collapse along the escarpment, occurred here in 1868 with a magnitude 7.9 and generated a 45-foot locally-generated tsunami. The conical rise on the coast is Pu'u Hou, a littoral (shoreline) cinder cone. The beach has a green cast due to olivine, one of three main minerals that comprise basalt. Coastal erosion often forms low cliffs within a bench of lava that reached the sea.

View of South Point (Ka Lae) from Pali o Kulani Lookout on Route 11, the Hawai'i Belt Road. Downwind of volcanigenic gases emitted from Kilauea, it's the southernmost locale of the Hawaiian Islands and of the fifty states. To the left is the steep Kahuku escarpment along Mauna Loa's Southwest Rift Zone with a wind farm along the cliff face that supplies 18,000 homes with green, renewable electrical power. Kilauea to the east has a pali related to slope failure along its rift zone. Wai'ahukini Beach was the main residence of great chief Kalaniopu'u in 1782.

SIMULTANEOUS AGGRADATION AND DEGRADATION
The morphology and structure of Hawaiian shield volcanoes (and likely others globally) results from the complex interaction between the accumulation of lava flows that enlarge the edifice and gravitationally-driven processes that degrade it ("volcano spreading"). As mentioned, it includes submarine landslides and slumps related to slope failure. These entities are ever-evolving and reconfiguring as the edifice grows, deforms and collapses. Deceptively hidden from view, an example is rift zone reconfigurations that can breathe new life into an old Post Shield volcano such as Mauna Loa, which allows it to grow additionally in size.

North-facing view of the expansive subaerial shield of Mauna Loa from Route 11, the Hawai'i Belt Road.

Back in the saddle, small Pu'u ka Pele cinder cone has a pleasing symmetrical simplicity. Recognizable by rock color and degree of vegetation, it resides on old flows from Mauna Kea. In the background, flows from Mauna Loa occurred within the last 1,000 to 2,000 years, while the dark-colored unvegetated flow originated from Mauna Loa in 1832.

THE HISTORY OF SADDLE ROAD
Route 200, known locally as the Saddle Road, unites the Big Island's east coast at Hilo with the communities of Kohala and Kona on the west coast. At 6,500 feet, the topographic high of the road is lofty enough for some individuals to experience difficulty breathing if not adequately acclimatized. As one climbs into the saddle, either on the ground or in the air, the vegetation visibly changes, reflective of the elevation, temperature and diminishing degree of rainfall. Plant life is largely non-existent on young, dark flows largely from 1935 and 1936 from Mauna Loa that headed west. The recent flows are a subtle reminder that the volcano is still active. 

The road also has an interesting history tied to World War II and the development of the island. Following the attack on Pearl Harbor in 1943, marines quickly built a primitive, non-civilian road into the saddle to access their newly established 133,000-acre Pohakuloa Training Area (below). The road also provided an inland evacuation route should the Japanese re-attack. The Bradshaw Army Airfield was constructed in 1956. Today, the training area serves as a firing range for the Army and Marine Corps ground and air units. 

The Saddle Road winds past the Bradshaw Army Airfield, Pohakula Training Area and row after row of quonset barracks. A tank trail parallels a portion of the Saddle Road. Several endangered species are in protected reserves in the saddle such as the Hilo Forest Reserve that is home to the bird Palila. 

In years past, the poorly maintained, oft-foggy, unpaved, windswept road had a high accident incidence to the extent that rental car companies specified it off-limits in their contracts. It has recently been fully re-paved and re-aligned, which prompted rental companies to sanction its use. Travelers can now safely traverse the island in an hour.

Heading east, the Saddle Road ascends Humu'ula Saddle and slices through a portion of Mauna Kea's cinder cone field. The low-profile slope of massive Mauna Loa rises on the horizon. The saddle consists of coalesced and interbedded flows from both Mauna Kea (foreground) and Mauna Loa (background).

The lunaresque landscape of the Saddle facing Mauna Loa

ISLANDS OF LIFE AND SANCTUARIES OF BIODIVERSITY AND PRESERVATION
Within the saddle, the patchwork of intermingled flows from Mauna Loa have encircled slightly elevated topographical areas and formed "islands" in a sea of lava called kīpukas. Within the "protected" locale, they contain soils and house a succession of vegetation that provides a habitat for plants and animals in this otherwise inhospitable environment. They have become a natural laboratory for studying insular biogeography (such as ecology, species richness, food web control and biotic resistance to invasiveness). The concept was originally applied to oceanic islands and first developed to a large extent by Darwin and Wallace. 

On Mauna Loa's east slope, a patchwork of new flows meet old, creating insular kīpukas in between.

PU'U HULUHULU
Humu'ula Saddle, via the Saddle Road, provides access to the summit of Mauna Loa via the Mauna Loa Observatory Road, the summit and astronomical observatories of Mauna Kea via the Summit Road, and cinder cone-kipuka Pu'u Huluhulu, immediately astride Saddle Road, all of which are within Hawai'i Volcanoes National Park. Pu'u Huluhulu (meaning "hairy hill") is a 60 m high cinder cone that is surrounded by pahoehoe flows from Mauna Loa, most recent as 1935. 

Acacia koa trees (foreground) on cinder cone-kipuka Pu'u Huluhulu

By composition, Huluhulu's basalts are alkalic, and since Mauna Kea and not Mauna Loa is in the Post-Shield Stage, it originated from Mauna Kea. A quarry at the base of the cinder cone exposes a remarkable dike of tholeiitic basalt that intruded Huluhulu. Because of its chemistry, its source had to be from Mauna Loa.

Koa trees on the trail that leads to the summit of Pu'u Huluhulu. Although not that high, the view of the lava field is spectacular.

The kipuka is also an ideal sanctuary for rare forest birds and the nēnē, an endemic Hawaiian goose and state bird that has endured a long struggle against extinction. It also possesses a remnant of a dry montane koa forest, an endemic flowering tree in the pea family once common at mid-elevations on the island, but was reduced to 10% by logging, fire and livestock pressure. It's another ecological story heard frequently heard throughout the islands. Acacia koa was used by early Hawaiians to build dugout outrigger canoes and later, ukuleles and Hawaiian guitars.

KILAUEA IN SIGHT
Having traversed Humu'ula Saddle and a myriad of lava flows on the east flank of Mauna Loa, the ascending flume of gas in the distance is a sure sign that Kilauea volcano is near. Each of the remaining four subaerial volcanoes on the island possess a summit crater, although many are obscured by eruptions that have subsequently masked their presence. In contrast, Kilauea's summit is marked by a small (although it likely seems large to visitors), two by three-mile, circular caldera, an explosion or collapse-induced summit depression enclosed by a set of arcuate faults. 

Through either process, the magma chamber is thought to have evacuated its contents during the formation of the caldera. Being sourced by the mantle, the caldera has remained extremely active and has been erupting continuously since 1983. Most geologists accept the date of 1790 when Kilauea's caldera formed from a crater that collapsed of unknown dimensions.

Facing south from the saddle, the outer rim of Kiluaea caldera and the fuming Halema'uma'u pit crater is clearly visible. The wind is carrying Kilauea's vog directly toward the chopper. Lava flows in the foreground have emanated from Mauna Loa off to the right. Notice the "islands" of kipuka surrounded by more recent flows.

In Post I (here), I reviewed important Hawaiian geography and discussed two prominent antithetical hypotheses regarding the island chain's evolution. The post ended with my arrival on the Big Island and my observations of the volcanic landscape during our descent. In this, Post II, we traveled from north to south on the Big Island from the Waimea Plain between volcanoes Kohala and Mauna Kea to the Humu'ula Saddle between Mauna Kea and Mauna Loa. In Post III, we'll fly directly over fuming Kilauea and turn east along its hyperactive East Rift Zone. To follow in Post IV, we'll cruise over the coastal town of Hilo and head north along the island's east seacliffs to the gorges of the Kohala Mountains back to the heli-port.

Aloha!

RECOMMENDED PRINTED SOURCES OF INFORMATION
This admittedly exhaustive list includes material on Hawaiian shield volcanoes, Pacific plate tectonics, hotspots, mantle plumes, theories on melting anomalies, mantle dynamics, Hawaiian glaciation, and basalt geochemistry and geophysics. The scientific articles, special papers, books, field trip guides and maps were used as reference information in the writing of this post. 

•  A Brief History of the Plume Hypothesis and its Competitors: Concept and Controversy by Don L. Anderson and James Natland, GSA, Special Paper, 2005.
• A New Insight into the Hawaiian Plume by Jianshe Lei and Dapeng Zhao, Earth and Planetary Science Letters, 2006.
• Annals of the Former World by John McPhee, 1998.
• A Possible Origin of the Hawaiian Islands by J. Tuzo Wilson, Canadian Journal of Physics 41, 1963.
• Archipelago - The Origin and Discovery of the Hawaiian Islands by Richard W. Grigg, 2014.
• Convection Plumes in the Lower Mantle by W.J. Morgan, Nature 230, 1971.
• Deep Mantle Convection Plumes and Plate Motions by W.J. Morgan, Bull. Am. Assoc. Pet. Geol. 56, 1972. 
• Did the Atlantic Close and Then Reopen? by J. Tuzo Wilson, Nature, v. 211, 1966.
• Divergence Between Paleomagnetic and Hotspot Model Predicted Polar Wander for the Pacific Plate with Implications for Hotspot Fixity by William W. Sager, Texas A&M University, Revised Draft 23, 2006.
• Eruptions of Hawaiian Volcanoes - Past,Present and Future, USGS, General Information Product 117, 2014.
• Evidence From Islands on the Spreading of Ocean Floors by J. Tuzo Wilson, Nature Publishing Group 197, 1963.
• Explore the Geology of Kilauea Volcano by Richard Hazlett, 2014.
• Extensional Tectonics and Global Volcanism by J. Favela, Javier and D.L. Anderson, in Problems in Geophysics for the New Mellenium, 2000.
• Fast Paleogene Motion of the Pacific Hotspots from Revised Global Plate Circuit Constraints by C.A. Raymond et al, History and Dynamics of Plate Motions, edited by M.A. Richards, R.G. Gordon, and R.D. van der Hilst, pp. 359-375, 2000.
• Geologic Map of the State of Hawaii by David R. Sherrod, John M. Sinton, Sarah E. Watkins and Kelly M. Blunt, USGS, Open File Report 2007-1089.
• Hawaiian Volcanoes - From Source to Surface by Rebecca Carey et al, AGU, 2015.
• Hawaii Volcanoes National Park - Geologic Resources Inventory Report, NPS, 2009.
• Hawaiian Xenolith Populations, Magma Supply Rates and Development of Magma Chambers by D.A. Clague, Bulletin of Vulcanology, 1987. 
• How Many Plumes Are There? by Bruce D. Malamud and Donald L. Turcotte, Earth and Planetary science Letters, 1999.
• Geochemistry of Lavas from the Emperor Seamounts, and the Geochemical Evolution Hawaiian Magmatism from 85 to 42 Ma by M. Regelous et al, Journal of Petrology, Vol. 44, 2003.
• Geology of Hawaii - Hofstra University Field Trip Guidebook by Charles Merguerian and Steven Okulewicz, 2007.
• Hotspots and Melting Anomalies by Garrett Ito and Peter E. van Keken, Treatise on Geophysics, 2015.
• Illustrated Geological Guide to the Island of Hawaii by Richard C. Robinson, 2010. 
• Is Hotspot Volcanism a Consequence of Plate Tectonics? by G.R.Foulger and J.H. Natland, Science, Vol. 300, 2003.
• New Evidence for the Hawaiian Hotspot Plume Motion Since the Eocene by Josep M. Pares and Ted C. Moore, Earth and Planetary Science Letters, 2005.
• Oceanic Island Basalts and Mantle Plumes: The Geochemical Perspective by William M. White, Department of Earth and Atmospheric Sciences, Cornell University, Reviews in Advance, 2010.
• On the Motion of Hawaii and other Mantle Plumes by John A. Tarduno, Chemical Geology, 2007.
• Plate Tectonics by Wolfgang Frisch, Martin Meschede and Ronald Blakey, 2011.
• Plates vs Plumes - a Geological Controversy by G.R. Foulger, Wiley-Blackwell, 2010.
• Pleistocene Snowlines and Glaciation of the Hawaiian Islands by Stephen C. Porter, Department of Earth and Space Sciences, 2005.
• Plumes, or Plate Tectonic Processes by G.R. Foulger, Astronomy and Geophysics 43, 2002.
• Revision of Paleogene Plate Motions in the Pacific and Implications for the Hawaiian-Emperor Bend by Nicky M. Wright, GSA, Geology, 2014.
• Roadside Geology of Hawai'i by Richard W. Hazlett and Donald W. Hyndman, Mountain Press Publishing Company, 1966.
• Superplumes or Plume Clusters by G. Schubert et al, Physics of the Earth and Planetary Science Interiors, 2004.
• The Evolution of Mauna Kea Volcano, Hawaii: Petrogenesis of Tholeiitic and Alkalic Basalts by F.A. Frey et al, Journal of Geophysical Research, 1991.
• The Hawaiian-Emperor Volcanic Chain. Part I. Geologic Evolution by D.A. Clague and G.B. Dalrymple, Volcanism in Hawaii, Geological Survey Professional Paper 1350, 1987.
• The Mantle Plume Debate in Undergraduate Geoscience Education: Pverview, History and Recommendations by Brennan T. Jordan, Department of Earth Sciences, University of South Dakota, in Mantleplume.org. 
• The Plate Model for the Genesis of Melting Anomalies by Gillian R. Foulger, Mantleplumes.org, 2006. 
• Tectonics - Continental Drift and Mountain Building by Eldridge M. Moores and Robert J. Twiss, University of California at Davis, 1995. 
• The Bend: Origin and Significance by Rex H. Pilger, GSA Bulletin, 2007.
• The Plate Model for the Genesis of Melting Anomalies - Chapter 1 by G.R. Foulger, GSA, 2007.
• Three Distinct Types of Hotspots in the Earth's Mantle by Vincent Courtillot et al, Earth and Planetary Science Letters 205, 2003.
• Through Thick and Thin by Neil M. Riber, Nature, Vol. 427, Barberry 2004.

NOTEWORTHY REFERENCES ON THE WEB
There's a ton of stuff on the web, but somehow I always ended up at these sites.

• The Hawaiian Plume Project (here)
• The USGS Hawaiian Sites (here)
• Mantle Plumes from the Platist's perspective (here) 
• National Park Service site (here) 
• USGS Hawaiian Volcano Observatory (here) 
• On Wayne Ranney's blog, his well photo-documented field excursions always make you feel like you are right there (here) and (here)