|Halema'uma'u pit crater within Kīlauea caldera is hallowed ground to Hawaiians.|
|Artist Arthur Johnsen's version of Pele from Wikipedia|
|Yours truly with one of Sunshine Helicopter's Black Beauties|
|The Hawaiian archipelago includes an oceanic mix of seamounts, atolls and islands. |
Numerous seafloor topographic features appear such as fracture zones, and the Hess and Shatsky Rises.
|Computer generated, color enhanced, refined image of Lōʻihi|
|Numerical simulation of a thermal plume. (Farnetani, 1997)|
|Three-dimensional simulation of plume head arriving beneath the Hawaiian hotspot. |
Colors signify predicted mantle temperatures. (Maxim Ballmer,SOEST/UHM)
|Halema'uma'u pit crater within the Kilauea caldera |
Does Kilauea sit atop a mantle plume or is there another explanation
for the Hawaiian Island's intraplate, age-progressive volcanic track?
|My front walkway in February|
My first sighting of Hawai'i from our passenger jet was the island of Hawai'i with four out of five shield volcanoes nudging above the cloud deck. You can just make out the outline of the island's rugged northeast coast (below). To not confuse the name of the island with the name of the state, everyone refers to it as "The Big Island." Each of its five volcanoes began their growth from the seafloor, emerged from the waves, and coalesced to form a single island over the span of some 800,000 years.
Concealed by clouds, the east flank of Kohala (bottom right) faces the rainiest side of the island, which has carved it into dramatic, basalt-layered, near vertical-walled gorges with pendulous waterfalls at every turn. Kohala is the island's most eroded, most gorge-dissected, northernmost and oldest subaerial volcano, having emerged from the sea ~500,000 ka. It reached ~31 miles in width before erosion and subsidence took its toll. Its most recent eruption was ~120,000 ka. Plumists theorize that Kohala has migrated far enough from the hotspot that it is the least likely to re-erupt of the island's volcanoes.
|We're facing the island of Hawai'i toward the southwest from about 20,000 feet. Poking above the clouds, four of its five volcanoes are in view. At the moment of this photo, the island of Maui could be be seen out of the right side of the plane.|
Mauna Kea (center above) is appropriately called the "White Mountain" with remnant winter snows on the summit. You can ski, but there are no lifts or lodges. Someone will have to drive a 4WD vehicle to take you up. It's the highest mountain in the island chain at 13,979 feet but not the most massive. That honor goes to Mauna Loa, the "Long Mountain", the planet's largest volcano in mass and volume measured from the seafloor (right rear). In 1975, Mauna Loa awoke from dormancy with a single-day eruptive event and again in 1984 with a flank eruption that threatened the east coast city of Hilo.
On the horizon (far right), lowly Hualalai clings to the west coast barely 11 miles from the Kona Airport, our immediate destination. The youngest and fifth volcano is Kilauea, hidden behind Mauna Kea and collapsed into a caldera. It's been erupting for 30 years in various forms with lava lake overflows, cinder cone eruptions and flank fissure eruptions emitting steam, gas plumes and an eerie red glow at night. That makes it the most active volcano in the world both temporally and volumetrically, and the only volcano in the entire island chain that is currently active subaerially.
DESCENDING ON THE DRY, LEEWARD KOHALA COAST
Turning south, our plane followed the Kohala Coast in the dry rainshadow of Kohala. On this western side of the island, the vegetation is noticeably brownish. Visible at this altitude and in stark color-contrast, a dozen or so upscale hotels have bulldozed 20 golf courses out of the barren lava flows that blanket the landscape.
The aridity, sparse vegetation and desert-like climate is due to orographic precipitation, caused by the interaction of ocean temperatures, prevailing winds and lofty volcanic topography. Prevailing trade winds acquire moisture from the warm Pacific waters. Upon reaching the islands from the northeast, the moist air rises, cools, condenses and rains on east-facing, windward slopes of the volcanoes but not on their summits, which are mountain-top deserts. On west-facing leeward slopes, the warm, dry air descends creating an Arizona-like climate. The effect is most dramatic on the Big Island with the tallest volcanoes.
|Annual Precipitation on the Island of Hawai'i|
The majority of precipitation is on the east and northeast sides of the island that faces the "trades",
while the west and southeast sides enjoy a desert-like climate.
Modified from Hawaii-Guide.com
Thus, the leeward side of the island is sunny and dry, while the windward side of the island is rainy and wet. You can see the differences in the erosion of the landscape and the location of the waterfalls, the number of streams that reach the coast, the type of crops that are grown, the wildlife, cloud development, the location of the resort hotels and the natural vegetation - sparse, scrubby and brown on the west and lush, green tropical rainforests on the east. Our waitress at a restaurant in Hilo on the east coast said that when she wants to work on her tan, she drives an hour or so west. The following montage says it all. Each locale is separated by only 50 miles as the crow flies.
Minutes from the airport, one million year-old Mauna Kea dominates the landscape. The volcano hasn't erupted in 4,500 years but is seismically active and capable of re-eruption. The arbitrary cut-off for volcanic extinction is 10,000 years, since the last ice age, even here in Hawaii. No visible caldera exists on the summit, but the ridge arrangement of cinder cones implies the presence of one, which was obliterated by the cones and their pyroclastic debris. It's past the active stage of edifice-building, typified by its over 300 cinder cones seen in profile. Each cone is asymmetric in keeping with the direction of the "trades" from the northeast.
Curiously, the 'trades' are also responsible for low clouds that blanket the landscape. Their formation is induced by a temperature inversion where a pronounced moisture discontinuity exists 50-70% of the time between 4,000 and 5,000 feet. The inversion embedded in the moving air suppresses upward flow, thereby restricting cloud development to the zone below the inversion. Towering clouds form along the mountains where the incoming trades converge as it moves up a valley and is forced up and over the mountains to heights of several thousand feet.
Mauna Kea's summit atmosphere is extremely dry and disturbance and cloud-free for optimal celestial viewing. Astronomers from eleven countries have assembled a 2 billion dollar-collection of 13 of the world's largest observatories on the summit for optical, infrared and sub-millimeter astronomy. Recently, there has been strong local opposition by Native Hawaiian, environmental and cultural groups to another observatory planned (a $1.3 billion Thirty Meter telescope, ten times more powerful than the Hubble) and an Army helicopter landing zone for high altitude training to be built on Mauna Kea and Mauna Loa's sacred summits.
|The twin W.M. Keck Observatory domes atop Mauna Kea are among the largest optical telescopes in use with 33-foot primary mirrors.|
SWAYING PALMS, POUNDING SURF, TURQUOISE WATERS AND MILES OF SAND
The prominent tongue of lava (below) originated from vents along the flanks of Kohala volcano and continues well beyond the water's edge. This region of the Kohala Coast is fronted by offshore fringing reefs and numerous pocket sandy beaches. A paucity of sediment-carrying perennial streams have conferred the west side with the cleanest and clearest water. Because of its clarity and the island's geological youth, it has the most live coral of the islands (57% or 29 sq. mi.).
Terrigenous sediment run-off and deposition on reefs significantly affect their health by blocking light and inhibiting photosynthesis, smothering and abrading the coral, and triggering macro-algae growth. In Hawaiian mythology, corals were the first creature that came into being before any higher forms emerged. Their importance is also ecological and recreational. Warm, calm and clear waters have made fishing, snorkeling and scuba diving a multi-million dollar industry (~$385 million in 2002).
|A dirt road cuts across a large platform of lava and connects remote and pristine Mahai'ula and Makalawena Beaches.|
WHITE, RED, GREEN AND BLACK SAND BEACHES
The varied colors of Hawai'i's beaches convey the geological story of the islands. Coral reefs flourish along older more stable, volcanically-quiescent coasts on the Big Island and the older islands of the chain progressing to the north, where water is sediment-clear and shallow to the sun.
Atoll formation was described as early as 1836 in the writings of Charles Darwin about the islands of Tahiti. As the Hawaiian islands age, erode and subside beneath the sea, they provide an environment for the formation of an encircling-ring of coral. Waves that pound offshore reefs and pulverize shells on the seafloor provide beaches with a steady supply of fine-grained, beige to yellowish calcareous sand. The small cobbles and smooth pebbles of black vesicular lava pleasantly clink underfoot while strolling on the beach.
Hualalai emerged from the sea prior to 300,000 years and is considered potentially dangerous having erupted in 1801. In fact, the airport and neighboring coastal communities are built on the most recent and underlying flows from 1,500 to 3,000 years ago. South of the airport begins the Kona Coast in the heart of the leeward side of the island in the rainshadow of Hualalai, Mauna Kea and Mauna Loa, which even further insulate the coast from moisture-bearing winds.
What I thought was atmospheric haze on the Kohala Coast turned out to be vog, an odorless mix of volcanic gases, largely sulfur dioxide and water vapor carried some 35 miles by the wind from distant Kilauea to the south. The entire island is monitored for air quality by the state, and health advisories are issued if a plume of gas reaches dangerous levels. Persistent, gas concentrated plumes generated by Halema'uma'u pit crater at Kilauea and its cinder cone Pu'u 'O'o have resulted in the closure of downwind roads in Volcanoes National Park.
TROUBLE IN PARADISE
Clumps of straw-colored fountain grass provide a striking color-contrast on the overlapping patchwork of pre-historic reddish-brown and relatively fresh, black lava flows that blanket Hualalai (below), but its an unwanted, invasive species. Introduced by man in the 1920's from Africa as an ornamental plant and still sold in nurseries, its has "escaped" to wilderness areas such as Hawai'i but also Arizona, Nevada and California. It outcompetes indigenous plants for water and space in pasture lands and is a fire threat.
The story of fountain grass typifies Hawaii's ongoing struggle to prevent the introduction of non-indigenous species, prevent the extinction of native species and reverse the island's declining biodiversity. Prior to human intervention, Hawaii's geographical isolation and varied topography have been the source of evolution and adaptation amongst the many lifeforms that reached the islands via the wind, ocean currents and attached to migratory birds. Unique birds and plants became perfectly suited to its environment and highly dependent on a fragile ecological balance to survive.
With the arrival of man, both intentional and accidental introduction of new species have upset that balance. The rate at which new species is introduced is estimated to be 2 million times more rapid than the natural rate. Thus, it is more crucial than ever that invasive, unwanted species be kept off the island, which accounts for the rigorous screening we experienced at the airport, even on domestic arrivals. Volcanoes National Park on the Big Island is a highly protected environment of preservation.
Another non-indigenous example is the weasel-like Asian mongoose, introduced to sugar plantations in 1872 to control the destructive rat population that likely arrived on Polynesian canoes and later on European and American sailing vessels. Unfortunately, mongoose are diurnal and rats are nocturnal. They both have no natural predators in Hawaii and subsequently have overrun the island. I was amazed to spot a mongoose in downtown Hilo at noon scurrying across the main street between cars. Unfortunately, both have a taste for the eggs and hatchlings of native birds and endangered sea turtles. They also carry leptospirosis and other disease-producing bacteria in their droppings, which has entered some freshwater streams. And so it goes.
PLEASE STAY TUNED FOR POST PART II
The Hawaiian Island chain inspired the theory of hotspots and mantle plumes. The ease of access and frequency of volcanic activity on the island of Hawai'i have established it as a type locality for basaltic volcanism; however, much is still unclear and unknown such as the fundamentals of how Hawaiian volcanoes actually work, the structure of the mantle and the functionality of thermal plumes, if they really exist.
In posts Part II-IV, I'll cover my geo-heli-tour of the island of Hawaii. Here's a small sample of a video I took of a vegetated cinder cone as we climbed into the lofty Humuʻula Saddle between Mauna Kea and Mauna Loa. That's Mauna Loa in the distance.
RECOMMENDED PRINTED SOURCES OF INFORMATION ON THE HAWAIIAN ISLANDS
This rather lengthy 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. Have fun!
• 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.
• 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: http://igppweb.ucsd.edu/~gabi/plume.html
• The USGS Hawaiian Sites: http://search.usa.gov/search?affiliate=usgs&utf8=%E2%9C%93&query=hawaii&commit=Search
• Mantle Plumes from the Platist's perspective: http://www.mantleplumes.org
• National Park Service site: http://www.nps.gov/havo/index.htm
• USGS Hawaiian Volcano Observatory: http://hvo.wr.usgs.gov
• On Wayne Ranney's blog, his well photo-documented field excursions always make you feel like you are right there: http://earthly-musings.blogspot.com/2011/06/hawaiian-geology-at-haleakala-crater.html and http://earthly-musings.blogspot.com/2011/06/trip-around-island-of-oahu.html