2013 Geology Posts That Never Quite Made It

Ancient West African Crust in Boston; Enigmatic Beach Sands of Florida; Living Fossils in Backbay; Cretaceous Oysters in New Jersey; Alpine Bogs in New Hampshire and a Precambrian River in Newton Center, Massachusetts

Every blogger knows the challenge. What shall I blog about next? What photos should I use? By the time the end of the year rolls around, there are always a few posts that never quite made it. And so, with this final post of the year, here they are from here and there. Please visit the same for 2012 here.

January
Flying High Above Boston’s West African Harbor Islands

Looking frigid and uninviting in mid-winter, Boston’s Harbor Islands are best explored during the summer months. The harbor is sprinkled with 38 of them, most designated as National Recreation Areas. Many have fascinating histories such as Georges Island (apostrophes are not used) with Civil War-era Fort Warren used as a Confederate prison and its resident ghost, the Lady in Black. Little Brewster is home to Boston Light, the oldest continually used lighthouse in the U.S. from 1716. Worlds End has plantings and roads by legendary 19th century landscape architect Frederick Law Olmsted, the designer of Central Park in NYC and Boston's Emerald Necklace park system. There’s even an abandoned, off-limits Nike missile silo on Long Island.

As for the region’s geology, Boston Harbor is a glaciated structural basin that has been inundated and modified by post-glacial sea level rise in the last 15,000 years. It contains dozens of exposed and submerged Pleistocene-age drumlins and other glacial features modified by coastal processes. The bedrock crops out at numerous locations and consists of the Late Proterozoic Boston Bay Group, rocks of the Avalonia terrane that accreted to Laurentia during the Middle Paleozoic.

The group consists of fine-grained clastics of the Cambridge Formation (“Argillite”) and coarse-grained clastics of the Roxbury Conglomerate better known as “puddingstone”, the Commonwealth’s state rock. The terrane of Avalonia rifted from its peri-Gondwanan, Southern Hemisphere-berth off the northern edge of the West Africa craton (although some advocate a northern South America provinence). It then drifted some 6,000 miles during the Ordovician across the Iapetus sea to its present location in Boston Harbor, accreting (attaching) in the process to a large portion of the Appalachian orogen along Laurentia’s northeast coast. 

February
On an Appalachian-Derived Beach at Fort Lauderdale

This Fort Lauderdale beach scene is far more welcoming meteorologically this time of year. It depicts a commonplace entity with the warming climate – beach erosion and restoration. Sediment (mostly sand) is typically lost through longshore drift (movement of material by waves that approach at an angle to the shore but recede directly away from it) and from changing ocean currents and storms. A wider beach reduces damage to coastal structures by dissipating energy across the surf zone. It also protects upland structures and infrastructure from storm surges, tsunamis (not on this passive marginal coast) and unusually high tides.

Of course, Floridians will need to deal with the issue that everyone must confront, rising sea levels from melting glacial ice. It won’t be the first time it has risen. Fluctuating glacial periods of the Pleistocene triggered vacillating high seas that periodically flooded coastal plains. Before that, during the Cretaceous, North America’s central continental and coastal lowlands were completely submerged by global high seas of the Tejas transgression.

By the way, Lauderdale’s beaches are composed of brownish, quartz sand not whitish, calcium carbonate, which is not what one would expect considering Florida’s carbonate-platform heritage. Silicon dioxide-rich sand was transported downbeach from the eroding Appalachians Georgia-way by longshore currents during the Cenozoic. Next time you stroll along the beach further south, check out a handful of sand. It gets whiter as its carbonate content increases with distance from its granitic source up north.

April
Living Cretaceous Fossils in Bloom in Boston’s Backbay

The annual explosion of pink and white magnolias in bloom is one of Boston’s first rites of spring. The city's floriferous trees have more to offer than large flowers, showy colors and fragrant scents. There's a tale of evolution to be told here.

You see, beetles pollinate magnolias, not bees as one might expect. Bees were not around in the mid-Cretaceous (about 100 million years ago), when magnolias were evolving. That pollinator relationship has changed little over the millennia since the co-evolution (mutual evolutionary influence) of insects and angiosperms (flowering plants). Magnolia flowers don't produce nectar, the sugary secretion that encourages insect visitation (and hence pollination). They do produce large quantities of pollen that's high in protein, which beetles use for food, and in the process, cross-fertilize (transfer) pollen from the male anther of one flower to the female stigma of another. The high proportion of beetle-pollinated systems within the Magnolia family has perpetuated the long-standing theory that modern flowers were derived largely from beetle-pollinated proto-angiosperms. Indeed, many paleobotanists have devoted their attention to plants such as magnolias in their attempts to unravel the events of angiosperm evolution. 

Magnolia's ancestral floral characteristics include: its large blossom with its tepal structure (magnolia's petals and usually green sepals in higher plants all look alike); its central, cone-like receptacle of spirally-arranged, male stamens at the base and similarly-arranged spiral, female carpels; its radial symmetry; its actinomorphism (floral parts similar in size and shape); and its leathery beetle-durable petals. 

One of many botanical classification systems, Cronquist's interpretation assigns magnolias to the most archaic positions of all living angiosperms, the subclass Magnoliids, along with water lilies and buttercups. The concept that magnolias are amongst the most basal angiosperms has been refuted by higher-level phylogenetic analyses, yet they remain one of the most important lineages in the early radiation of angiosperms. Appearing long before the radiation of flowering plants, Charles Darwin called their abrupt appearance in the fossil record “an abominable mystery.” What's more, the magnolia qualifies as a "living" fossil, having changed little since it first appeared.

By the way, magnolias acquired their name from the 17th century French botanist and physician Pierre Magnol. Now back to enjoying spring in Boston!  

June
Luxuriating in the Grenville-Age High Peaks of the Adirondacks

This High Dynamic Range photo of glacial Heart Lake was taken from the summit of lowly Mount Jo in the High Peaks region of the Adirondack Mountains in uppermost New York State. The tall peak to the right is Algonquin. Colden is the rock slide-scarred summit in the center, and to the left, Mount Marcy is the highest in the state, each separated by Precambrian faults re-activated during the Paleozoic.

We see almost two billion years of geological scenery in the making, beginning with the meta-anorthosite bedrock that emplaced during the Grenville orogeny. The protracted, multi-phasic tectonic event culminated with the formation of the Late Proterozoic supercontinent of Rodinia and a transglobal Grenville Mountain spine. Rodinia’s subsequent fragmentation in the latest Proterozoic formed two megacontinental siblings: smaller equatorial-positioned Laurentia and larger australly-located Gondwana. The two incrementally re-assembled throughout the Paleozoic into the supercontinent of Pangaea along with its Appalachian Mountain spine.

In the Late Cretaceous, the peneplaned Grenville’s, now internal to Laurentia, began to dome upward triggered by the region's proximity to the Great Meteor Hotspot that tracked southeastward from Canada beneath the drifting North American plate. The hotspot crossed the Mid-Atlantic Ridge, after tracking beneath the North American plate generating seamounts in its path, and is currently off the coast of Africa beneath the African plate.

Having been glacially sculptured during the ice ages of the Pleistocene, the Adirondack’s ascent of “new mountains from old rocks” (namely Grenville basement crust domed into a mountain range) possibly continues to this day. What’s more, we geologically recognize that the Adirondack’s (located cratonward) are distinctly non-Appalachian in origin (paralleling the coast)!

July
A Summer’s Wade in the Late Cretaceous Marl of Big Brook

This lazy stream, a “piddly little dribble” in the words of the New York Paleontological Society's field guide, courses through one of the oldest and prolific collecting sites for marine fossils on the East Coast. Collectors, both amateur and professional, have been extricating both vertebrate and invertebrate faunal remains out of the clear-flowing waters of Big Brook in Monmouth County of coastal Central New Jersey for well over a hundred years.

The diverse, age-spanning list includes Cretaceous bullet-shaped belemnite guards (a squid-like mollusc), brachiopod, oyster and clam shells, steinkerns (shell casts), hadrosaur (washed down from the mainland), shark and mosasaur teeth, alligator scutes, Pleistocene sloth and mammoth remains, Holocene Lenape arrowheads and even Colonial nick-knacks such as smoking pipes and pottery.

As the brook wends its way to the sea through farmlands, forests and the gentrified estates of rural New Jersey, it flows through a Late Cretaceous continental shelf setting and dissects its way down through Pleistocene and Holocene alluvial surface-overburden along the way. Although the banks are off limits for active fossil exploration, the brook does most of the work for fossil hunters as the bounty virtually collapses in from the upland Navesink Formation and glauconitic Mount Laurel Formation of the streambed. All that’s needed to sift through the streambed is a wire-mesh screen, a garden trowel, a pair of waders and a little patience.

Simply park your car, stroll a short distance through the woods, step into the stream, and travel back in time 66 to 70 million years near the end of the Age of Dinosaurs! 

August
Monster Mushrooms in Chestnut Hill, Massachusetts



This astounding three-foot beauty appears like clockwork every August near the base of a massive oak in my Boston suburb of Chestnut Hill. The rather drab, cream-colored mushroom is intricately branched with overlapping caps, yet surprisingly emanates from a single stalk. Its mycelial network remains dormant beneath the soil until summer rains and heat cause the fungal “roots” to germinate into a gargantuan “plant” above the soil. It gives the impression of growing from the ground, but it actually has colonized the buried roots of the tree, making it parasitic.

Once considered to be plants, with which they share many traits, fungi actually belong to their own kingdom of classification. As for the mushroom (the fruitbody), it’s relationship to the parent fungus is as the apple (the fruit) to the tree. This Bondarzewia berkeleyi is a bracket fungus, so called because many within the family grow shelf-like from the sides of trees. Its reproductive spores are manufactured within tiny tubes on the underside of the fruitbody rather than within the more accustomed gills we're used to seeing. For this reason, species within this group are called polypores. If cut when fresh, the pores exude latex. It’s not considered edible because of its leathery and woody texture, not that you're tempted.

September
My Lofty Visit to an Alpine Bog in New Hampshire

Artificially located above the treeline due to ravaging fires in the early 19th century and below the climatic treeline of higher mountains in the region, this exquisite alpine bog hides on a corner of the summit of Mount Monadnock at the foot of the White Mountains of New Hampshire.

The tops of mountains, where the climate is cold, windy and rainfall is scant, are amongst the harshest biomes on our planet. Only a select few plants and animals can exist in these severe conditions. Depressions in the bedrock collect rain and retain what little soil exists on the summit, keeping it permanently saturated. The lifeforms encountered here are similar to those found in the arctic tundra further north. Well-adapted to the bog’s poorly-drained, nutrient-poor and acidic peat soil are Sphagnum mosses, which form a carpet on which the bog’s dwarf shrubs and herbs grow. Look for Deerhair bog sedge, sheep laurel and tufted cotton-grass interspersed with patches of Labrador tea, leatherleaf, cranberry and round-leafed sundew to name a few. 

Mount Monadnock’s rocky core at higher elevations is composed of highly metamorphosed schists and quartzites of the Devonian-age Littleton Formation, which extends well north into the White Mountains of New Hampshire. The mountain represents an overturned syncline derived from compressional forces exerted during the Acadian orogeny, the second of three tectonic collisions that created the northern Appalachians and contributed to the crustal growth of Laurentia (proto-North America).

As our planet experiences progressively warmer climatic conditions, alpine flora and fauna will be challenged as they attempt to progress to a higher elevation to survive. They can only climb so high before being eradicated from their biome. If changing climatic conditions regionally prevail globally, the lifeforms will become extinct. This occurrence, species extinction, has been going on naturally since life appeared on our planet, but we understandably become concerned when its thought to be anthropogenic (man’s fault).

Henry David Thoreau spent some time on Monadnock in the mid-1800's, writing in his journal about the regional botany and geology. There's supposedly a bog up here named for him. This might be it!

October
High Atop Laccolithic Katahdin in the Remote North Woods of Maine



Congratulations are in order! You’re approaching the flat Tableland of mile-high Mount Katahdin in the wilderness of northern Maine from its west flank. Notice the botanical succession you've witnessed with elevation: deciduous hardwoods in autumnal splendor that blanket the lowlands; evergreens foresting the mountain's slopes; and alpine tundral sedge in the foreground.

The bedrock of Katahdin is a Devonian-age laccolith that has achieved its lofty status through intrusive buoyancy, surface erosion and post-glacial isostatic rebound. Katahdin (Mainers and climbers in the know drop the “Mount” from the name) formed during the Acadian orogeny, the second of three tectonic collisional phases that built the Appalachian Mountain chain and contributed to the crustal growth of Laurentia, the Paleozoic continent of North America.

Once Pangaea fully assembled following the third orogeny, the Appalachians graced the supercontinent with a Himalayan-esque mountainous backbone. The pluton of Katahdin, along with the other regional peaks, emplaced within a sea of Late Silurian rock during the Acadian collision in what is thought to have been a retro-arc setting.

Getting here was no easy task, especially if you just trekked 2,180 miles along the Appalachian Trail from Springer Mountain in Georgia to this point at the trail’s terminus. But you're not quite finished. To reach the Tableland you still have to complete the “A.T.’s” final assault via the Hunt Trail’s Spur on a near-vertical, 

quad-burning, heart-pounding, lichen-encrusted, truck-sized boulder-strewn ascent of pink Katahdin granite. Once on the Tableland's plateau, you must strive for Katahdin’s penultimate summit of Baxter Peak, one of five that rim its three cavernous glacial cirques on its east flank.

"Press on. You’re almost there. The view is spectacular!”

November
The Remnants of Historic Fort Bowie within the Apache Pass Fault Zone

Apache Pass is a natural opening and low point at the juncture of the Dos Cabezas and Chiricahua Mountains in southern Arizona. Since prehistoric times, it’s been of importance to humans as a major travel route connecting the San Simon and Sulphur Springs Valleys.

Part of the Basin and Range physiographic province of southeastern Arizona, the surrounding mountains rise abruptly like islands of rock in an arid desert from relatively flat, sediment-filled basins that formed during an extensional tectonic regime about 20 million years ago. Even older is the Apache Pass fault zone, initiated over a billion years ago as strike-slip and more recently reactivated as normal faults during Basin and Range extension. Precambrian rocks on the southwestern side of the fault (on this side of the fort) have been moved upward relative to the Paleozoic and Mesozoic strata on the northeastern side (the hills just beyond the fort). Thus, the fort rests on Permian Horquilla Limestone of the Naco Group, while, amongst other rocks, the hills are Late Jurassic to Cretaceous Glance Conglomerates of the Bisbee Group. Erosion of the fault zone's shattered rocks formed the saddle of Apache Pass.

The Apache people, who arrived in America with their Navajo cousins sometime after 1000 AD, hunted and camped in the area, and drank from Apache Spring that emanates within the fractured and faulted rocks within the fault zone. With the arrival of the Anglos in the mid-1800’s, Puerto del Dado, the Spanish name for the “Pass of Chance”, became the site of Fort Bowie (actually the second) by 1868 to insure the safe movement of the Butterfield Overland Mail, a stagecoach and mail service that connected Memphis and St. Louis with San Francisco. Prior to this, the arduous route was by ship across the Gulf of Mexico to the Isthmus of Panama, and on to California via the Pacific Ocean. For years, the Apache Wars led by Cochise and later Geronimo of the Chiricahua Apache waged upon the U.S. military. It all ended in 1886 with Geronimo's surrender and expatriation to Florida, leaving the foundations of the fort to decompose into the landscape.

The region’s complex geologic history contributed to the strategic importance of the pass and delivered dependable water into the fracture zone. It's another reminder of the importance of geology and geographic setting in shaping the course of civilization and human history.

December

A Six Hundred Million Year Old West African Riverbed in Newton, Massachusetts

Oblivious to most passersby alongside Beacon Street, a major thoroughfare out of Boston, is a cross-section of an ancient streambed embedded within a cliff wall. The stream bed appears as a semi-circular channel outlined perfectly by fallen leaves. The transected bed and its banks consist of fine-grained, thinly-bedded, fissile (easily split along its planes) siltstone (mud rock) that displays a large infill of conglomerate rock over its entirety. The siltstone preserves the contours of an ancient landscape that was buried by subsequent deposition.

Upon close inspection, laminations within the streambed display whorls of sediment indicative of stream turbidity currents and slump features indicative of settling. The manmade wall at the top is composed of stacked conglomerate boulders.

The flat-lying rocks of the entire assemblage, being sedimentary, were deposited horizontally under the action of gravity. Subsequent to their deposition, compaction, cementation and lithification (conversion to solid rock), the assemblage and the rocks in the region were tilted by tectonic forces, which accounts for the angulation seen in the photo. These rocks belong to the Roxbury Conglomerate, a 2,000 foot thick formation of coarse arkosic sandstone with small to medium-size, rounded clasts (rounded fragments of stones). In 1830, the American poet Oliver Wendell Holmes likened the Roxbury to puddingstone, its common name, since it reminded him of raisins in English bread pudding.

The puddingstone's sandy matrix and rocky inclusions indicate they were deposited in a high-energy depositional and/or transport system such as a cascading mountain stream or a massive submarine flow. The Roxbury is exposed almost everywhere in the neighboring towns to the west and southwest of Boston. The channel's siltstone is a facies change, a clastless sediment within the Roxbury Formation. Along with the Cambridge Argillite (or Slate), the Roxbury Conglomerate comprises the sedimentary strata of the Boston Bay Group. As mentioned in the first vignette at the top of this post, the group was deposited on the microcontinent of Avalonia in an extensional regime, such as a faulted rift basin in Late Proterozoic-time between 595 and 540 million years ago.

Avalonia originated as an elongate volcanic island chain along the edge of the megacontinent of Gondwana, possibly of West Africa cratonic provenance in the southern hemisphere. Avalonia’s deeper basement is volcanic in origin, and, in the vicinity of the Boston Basin, they include the Brighton, Dedham, Mattapan, Lynn and Westwood granites, which underlie the rocks of the Boston Bay Group. During the Acadian orogeny, Avalonia welded to the continent of Laurentia about 370 million years ago. Can't get enough of the Roxbury Conglomerate? Check out my previous post here.

The "unnoticed" streambed is an example of my masthead statement at the top of my blog. "Geology is all around us, scarcely thought of as we go about our lives." Perhaps I should add, "but not by all of us!"

Happy New Year from Franklin the Border Collie (and Jack)!

High Dynamic Range digital photograph

The Adirondack Mountains of New York State: Part IV - Climbing the Geology of a Fault-Bounded Valley

This is post IV of my four-part series on the geology of the Adirondack Mountains. Please visit:
Part I – What's so unique about their geology?
Part II – What do we know about their geological evolution?
Part III - Climbing the Geology of the High Peaks

This early 1900's postcard depicts Lake Colden from Avalanche Pass in the High Peaks Region of the Adirondacks of northern New York State. Lake Colden is the first of three spillover-lakes that reside in a post-Pleistocene, glacially-scoured, fault-bounded valley between sheer cliffs of Middle Proterozoic Grenville metanorthosite.



On the first day of our geological exploration in the High Peaks Region, my daughter and I ascended Mount Wright and Mount Algonquin, the latter being the highest peak in the MacIntyre Range and second highest in the state. To visit that post, click here. On this day, we explored the waterforms immediately east of the MacIntyres.

 

FINDING FAULT
During the assembly of the supercontinent of Rodinia, Middle Proterozoic Grenville orogenic events laid a foundation of metanorthosite and associated rocks throughout the region. Many of the NE-striking faults within that basement may have begun as normal faults in the extensional environment that existed during the closing stages of the orogeny.

 

The faults that persisted within the Adirondacks were likely reactivated (and new ones created) during Paleozoic Alleghenian tectonic collisions, specifically during overthrusting of the Taconic Orogeny. Late Cretaceous thermal doming of the region of the future Adirondacks subsequent to passage over the Great Meteor hotspot also may have reactivated the faults. These events, from the Middle Proterozoic through the present, are explained in greater detail in my post Part II here. Today, the myriad of NE-SW faults influence the orientation of many of the ranges and waterways within the High Peaks Region.  

 

THE BIG PICTURE
The following three-photo panorama faces south towards the High Peaks. It shows the relationship of the NE-trending MacIntyre Range to fault-bounded Avalanche Pass on the east and Indian Pass on the west. The open flat in the foreground is a small portion of a post-glacial, dry lakebed called South Meadows. Many large lakes such as this were breached when their ice and morainal dams catastrophically broke open. Our trek to the lakes via Avalanche Pass began at Heart Lake, at the base of Mount Jo. 

  

You can also see the fault-trending relationships aerially on this image captured from Google Earth.  



ASCENT TO MARCY DAM AND POND 
At sunrise, we departed from the Adirondack Loj (spelled correctly) at Heart Lake (elevation 2,169 feet). After a two-mile upward grade, we reached Marcy Dam and its impounded Marcy Pond (elevation 2,346 feet). In 1999 Hurricane Irene wiped out a footbridge that crossed the dam, which was rebuilt downstream across Marcy Brook. The dam replaces one first built for the logging industry at the turn of the previous century.



A wooden, weather-beaten Marcy Dam without its footbridge impounds brook trout-stocked Marcy Pond at low stage.

LEGACIES OF THE PLEISTOCENE
The waters of Marcy Pond are a small part of the St. Lawrence Watershed. They flow north to Lake Champlain and the St. Lawrence River, the widest river in the world and a major shipping lane between the Great Lakes and the Atlantic Ocean. The Adirondack’s watersheds and their respective waterforms formed subsequent to the most recent recession of the Laurentide continental ice sheet in the Pleistocene about 16,000 years ago.

Late Cretaceous uplift responsible for the creation of the Adirondack range initially established a radial stream pattern in the mountainous, elliptical dome that formed. With subsequent downcutting to erosion-resistant, anorthositic bedrock, Grenville-age faults began to dictate the pattern of flow. Today, still radial on a grand-scale, a trellis pattern follows the many linear fault zones with lakes, rivers and streams directing their waters ultimately to the Atlantic either via the St. Lawrence or Hudson Rivers.

We’re standing on Marcy Dam looking south across rain-depleted mudflats of Marcy Pond. The pond serves the watershed north of Avalanche Pass which is directly ahead. Landslide-scarred Mount Colden forms the east side of the pass, but the pass divides the watershed to the north and south.



ACID RAIN
The waters of the Adirondacks are sensitive to deposition in the form of acid rain due to their topography, low neutralizing capacity of the lakes and streams, and the relatively large amounts of annual rainfall. Sulfur dioxide and nitric oxide emissions from the burning of fossils fuels not only rains down from the atmosphere as diluted acids but falls to earth in the form of particles, gases and aerosols. As a result, the quality of the water has degraded over the past century.

The situation is compounded by sulfur dioxide emissions that provide the material for the growth of bacteria which in turn convert mercury into a form that is bio-available to fish. It gets worse in that acid soils become depleted of calcium and other nutrients, and release aluminum into the surface waters. Although pollution reduction measures from Clean Air Act legislation have shown improvements, the forests and aquatic life have suffered considerably. 

An informative paper on acid rain deposition in the Adirondacks is here.

 

MOUNTAIN STREAM DYNAMICS
Above Marcy Pond, the trail to Avalanche Pass roughly follows Marcy Brook, again dictated by the underlying bedrock. Seen here at low-flow stage at a bend in the brook, the distribution and size of anorthositic cobbles and boulders in the streambed, and the tangled mass of vegetation hint at the high volume and velocity of water during a spring melt or severe thundershower.

In spite of its shallow gradient, notice the scouring of the banks and bed at the widest point of the channel, also the deepest. Erosion occurs at the outside of the bend (the cutbank), while slower velocities at the inside of the bend causes point-bar deposition (the slip-off slope). At low-stage and at the inside of the bend the stream lacks the power to carry its load of suspended sediment and detritus.

Physical characteristics of the stream also influence water quality, and therein, the variety and type of habitat that is available to support life. Also notice how the riparian vegetation in the bank zone is affected by the stream’s hydraulic geometry. Evergreens are thriving on the inside of the bend; whereas, mixed deciduous, herbaceous growth has colonized the outside (i.e. willows), the damper more saturated soil region. 



Viewed within the context of the geological time frame, the contribution to landscape evolution of a small stream such as Marcy Brook, which might flood only a few times a year, should never be perceived as inconsequential. Significant change occurs over geological periods of a thousand or a million years especially accounting for the many companion streams that exist within the watershed!

 

AVALANCHE PASS
Continuing on our ascent, we reached Avalanche Pass between the confining mountains of Colden and Avalanche. The pass serves as the drainage divide for waters flowing north to Lake Champlain and south to the Hudson River within the Upper Hudson Watershed. As we entered the pass, its lichen-encrusted, sheer rock walls of anorthosite increasingly closed in, and the wind picked up as it accelerated from the confinement.

This is the narrowest section of Avalanche Pass looking south with opposing walls of anorthosite separated by 100 feet. 

 

Backpackers have taken the time to construct this mini-cairn city which my daughter felt obligated to contribute to.

In keeping with its namesake, an enormous, jumbled-mass of vegetation and bedrock avalanched downslope from Hurricane Floyd in 1999 along a 600 foot-long rock slide on Mount Colden. Volunteers and professionals have industriously cleared a trail directly through it. This photo looks up the slide on Colden’s western face past the mountain of cut foliage. In winter, hikers and skiers must be attuned to the inherent dangers that lurk within the pass from avalanching snow.

Within the pass is a spruce swamp with boardwalks over the boggy ground which supports the rare fern Dryopteris fragrans. Occasional, rust-colored stagnant pools of water suggest iron-rich pyroxenes that eroded from anorthosite underwent oxidation and imparted a dark-brown, rust color to the water.

 

AVALANCHE LAKE
Once through the pass you emerge into the uppermost reaches of the Upper Hudson River watershed. You're about to receive a visual reward for your climbing efforts. Before you is spectacular, sparkling Avalanche Lake, the first of three spillover-lakes that lie in a chain within a fault valley. Avalanche Lake is supposedly the highest lake in the United States east of the Rocky Mountains at an elevation of 2,864 feet. I’ll let my industrious readers research that one.

This is an incredibly special and beautiful place in the High Peaks that evokes strong emotions when first seen. Framed by the precipitous mountain flanks of Colden on the east and Avalanche Mountain on the west, their rock-walls plunge directly into the lake. This view is from the beach looking south from the end of the lake. Barely visible at the far end of the lake is its outlet and an active beaver dam. 

Avalanche Mountain’s vertical face plummets a thousand feet into the lake’s western side. Notice the parallel jointing on the rock wall, some of which is curvilinear, composed of metanorthosite and anorthositic gneiss. Alleghenian orogenic collisions of the Paleozoic, most likely the Taconic, are responsible for these deformational features along with the reactivation of faulting that contributed to the formation of the valley. Also notice the pattern of exfoliation in areas of the cliff with a reverse-step pattern. Anorthosite shares this property with granite by eroding from the surface in layers like an onion. Around the lake mixed conifers and deciduous hardwoods luxuriate in remnants of glacial till, a mixture of clay, sand, silt and stone.

The following USGS topographic map illustrates the NE-trending fault-valley that contains the lakes of Avalanche, Colden and Flowed Lands (not seen), all south of Avalanche Pass. The closeness of the contour lines on Avalanche Mountain’s eastern face reflects its thousand-foot verticality. Faults within the Grenville basement served to weaken the bedrock. Following Late Cretaceous uplift and unroofing, the bedrock was more readily eroded and excavated by Pleistocene Continental ice sheets that slowly bulldozed through the region.

The system of spillover lakes is a product of the post-glacial watershed that was established. Surface water elevations are primarily controlled by the underlying bedrock elevation rather than the type of bedrock. As mentioned, a trellis drainage pattern has developed in response to the system of faults and is superimposed upon an outward-from-the-center radial pattern dictated by the Adirondack’s uplifted dome (see my post Part I here).  

  

LAKE COLDEN AND AVALANCHE PASS FROM THE SOUTH
From the trail along the lake's western shore, this two-photo panorama looks back to the north at Avalanche Pass and its defining and confining cliffs of Avalanche Mountain and Mount Colden on the west and east, respectively. The lake is also notorious for its double echo at this spot which we tested successfully. 

This Goggle Earth, northeast-facing, aerial-view of the fault helps to illustrate the orientation of Avalanche Pass and Lake to Avalanche Mountain on the west and Mount Colden on the east. Shear displacement along the fault on the western side is to the southwest. Notice the rock slides that have scarred the slopes of Mount Colden. Also notice the outlet-brook that flows from the lake's south end toward Lake Colden.

“HITCH-UP MATILDA!”
The trail south continues along the west side of the lake, but it’s nothing like you might expect. In two stretches where the cliff plummets straight into the lake the only way to construct a trail in the 1920’s was to bolt two, wooden catwalks to Avalanche Mountain’s rock-face. And that’s not all. Over a dozen wooden boardwalks and ladders lead you up, over and around massive boulders that have torn loose from above and littered the shoreline. It reminded me of the board game Chutes and Ladders from my youth.

As the 1868 story goes, a young woman named Matilda was being carried by a guide through the pass. As the water deepened, her sister repeatedly urged Matilda to “Hitch-up!” in order to remain dry. Such is the mountain lore of the Adirondacks.

  

THE TRAP DIKE OF COLDEN
Another surprise awaits the climber! Halfway down the lake on Hitch-up Matilda, Mount Colden’s famous and infamous “Trap Dike” comes into view across the lake. Dikes are conduits that transport molten, pressurized magma through fractures and weaknesses in the crust. Being less resistant to erosion than the anorthositic country rock through which it intruded, the dike has since weathered out upon its exhumation and exposure, leaving the gaping chasm that we see today. 

 

The dike appears as a deep, 80 foot-wide, vertical gash that extends from the lake to Colden’s summit, a distance of almost 2,800 feet. The dike's immense size is very deceiving with its length being twice the height of the Empire State Building. Look at the massive evergreens for scale. 

Although many hikers believe that you become ‘trapped’ once you enter the dike (which has some truth historically), the word is actually Swedish for stairs (trappa) referring to the “steps” that formed in the dike’s magma as it cooled and contracted. Geologically referred to as the Avalanche Dike, it was first explored by pioneering geologist Ebenezer Emmons in 1836 who described the experience of being within its vertical walls as of a "sublime grandeur.” Ebenezer made this sketch of "The Great Trap Dyke at Avalanche Lake" in 1883. 

DEFINING THE DIKE GEOLOGICALLY
Compositionally, the Trap Dike is a diabase of garnetiferrous metagabbro. The presence of garnet within the dike is a signature of high grade, granulite-facies metamorphism, and suggests that it intruded before the final metamorphic tectonic event to affect the Central Highlands Region.

The dike emplaced before anorthosite host-rock crystallization based on such characteristics such as sharp contacts with the anorthosite and its cross-cutting relationship. Its intrusion and metamorphism occurred during the protracted Grenville Orogeny, a billion years before the uplift of the Adirondacks into a mountain range in the Late Cretaceous. 

Although the Grenville Orogen was extremely complex, highly protracted and multi-phasic, for purposes of simplicity it can be subdivided into four major events: a subduction arc-collision, an episode of voluminous anorthosite and AMCG intrusion, a strong collisional event and an extensionally-dominated collapse of the orogen. The Trap Dike's gabbroic rock likely would have formed during anorthosite petrogenesis and its intrusion shortly after the host-anorthosite emplaced. For more information on anorthosite evolution, please visit my post Part III here.



A CLUE TO THE REGIONAL LANDFORM
The rock-type on opposite sides of Avalanche Pass is anorthosite, suggesting that the landform might simply have resulted from closely-spaced joints, of which there are many. The formative clue is revealed by Colden's Trap Dike which continues on the opposing side of the valley across the lake. Offset of the two dike-segments on either side confirms the landform is indeed a fault-valley, as is Indian Pass on the west of the MacIntyre Range between it and Wallface.

 

ROCK SLIDES OF COLDEN
Also of interest are the bare rock surfaces on Colden’s granite-like face. They are in fact landslide scars and are typical of many high peaks in the Adirondacks. The thin cover of soil that tentatively clings to the anorthosite 's rough surface is stabilized by vegetation but can become destabilized on steep slopes when saturated by heavy, unrelenting rains.

The Trap Dike serves as a natural funnel for runoff and slide material by channeling everything down to the lake. At the dike’s outlet a large debris fan extends out into the lake. So massive was the debris-flow from Hurricane Floyd in 1999 that it instantly raised the height of the lake ten feet, and in 2007 an avalanche on Colden blasted debris to the opposite shore. Historically, the earliest documented slides are from the hurricanes of 1869 and 1942.

This view of Colden’s west face was taken from Mount Algonquin on our climb the previous day. Old slides are distinguished from new by the color of freshly exposed plagioclase gleaming in the sunlight. The slides' funneling of material into the dike have deforested its lower half. The dike's vegetated upper portion appears as a depression and continues over the crest of Colden and beyond, as seen on the topo map (above). Remember that the dike continues to the west as well into the body of Avalanche Mountain, offset by faulting regionally. A second, smaller dike also has been found on Colden near its summit parallel to the foliation of the anorthosite.   

  

Aside from its prominence and topographic expression, Mount Colden's dike is not unique in these high peaks of the Adirondacks. For example, a billion years after the emplacement of the Trap Dike, swarms of gabbroic dikes formed during the Mesozoic rifting of the Atlantic Ocean, but they occur with greater abundance in the eastern Adirondacks, southeastern New York and throughout New England.

 

CLIMBERS BEWARE!
Since the first documented climb in 1850, the Trap Dike has become a classic and dangerous mountaineering route in the High Peaks, renowned for its steepness and difficulty especially in wet weather. It contains many large boulders and ledges to negotiate, and even a waterfall or two in the spring. Wet anorthosite, even with its rough texture, can be extremely slippery when wet.

Climbers heading for Colden's summit that bail out of the dike too early find themselves on a precipitously-steep, exposed-slope of 45º. “Stay in the dike, where the climbing becomes easier!” warn online climbing journals where the best spot to exit the dike is marked by a cairn. Overall it’s a non-technical, Class 3-4 climb, but many rescues take place when climbers get stuck or "trapped" in the dike, and many have lost their lives by literally falling off the mountain. Check out YouTube.com for climbing videos, but don't forget to look at the geology! 

 

AVALANCHE LAKE TO LAKE COLDEN
Continuing further on the trail, Avalanche Lake’s outlet at its south end provides a close look at a beaver dam and a tremendous view north toward Avalanche Pass. We’re looking directly up the fault!

Having departed from Avalanche Lake, we followed its outlet stream down to Lake Colden at an elevation of 2,766 feet. Colden is the second of three lakes in the chain within the fault-valley and the end of our journey into the High Peaks Wilderness. Beyond Lake Colden’s beaver-marsh, we’re looking north toward Colden with its rock slides. The trail continues on below Lake Colden along another outlet brook to the curiously named lake of Flowed Lands which drains south to the Hudson River and down to the Atlantic Ocean.  

Lake Colden ended our exploration of the chain of lakes within Avalanche "fault." A curious stream enters the Flowed Lands from the east called Opalescent Brook. The stream bed is renowned for its anorthosite filled with beautiful, blue-green iridescent labradorite that shimmers in the water. We were hoping to reach that point, but the trek got the best of us. The round trip was almost 12 miles and 8 hours, returning via the same route. Perhaps next summer!

 

 

"FOREVER WILD"
In spite of the fact that the Adirondack Park and Forest Preserve was established with the catchy phrase “Forever Wild” in 1885, the logging industry managed to denude vast areas that left the region susceptible to wildfires. In 1903 an estimated 600,000 acres of land burned in the Adirondacks including vast tracts of this High Peaks Watershed. Various conflagrations continued for an additional decade. Between rampant logging, forest fires and disruption to wildlife, much of the Adirondack wilderness laid decimated.

  

 

 

 

The Adirondack region was the "crucible of the American conservation ethic" at the turn of the twentieth century (The Great Experiment in Conservation by Porter et al, 2009). These days, tourism, timber and mining are the mainstays of the modern Adirondack economy. Yet, significant change is likely to be in the future of the Adirondacks as it continues to grapple with a shared vision of sustainability.

 

The mountains are actually wilder and more pristine now than they were a century ago. Today, the park's 2.6 million acres are heavily protected and well-managed. Its size is 6 million acres, larger than Yellowstone, Yosemite, Grand Canyon, Great Smoky and Everglades National Park COMBINED! 

 

“We do not inherit the earth from our ancestors;
We borrow it from our children.”
Native American proverb