Sunday, November 7, 2010

11-06-10 Mt. Jefferson: Felsenmeer & Glacial Geology

I finally, finally got North to the "Whites" again after what seemed like an eternity. On Saturday (11-06-10) I drove to the Cog Railway Base Station to meet Thom (pronounced Tom) Davis (P. Thompson Davis) a friend and Professor of Geology at Bentley University in Boston, MA. Our intention was to hike up Mt. Washington via the Ammy to tour the boulder fields, or felsenmeer, on the summit cone. Thom had generously offered me time from his busy schedule to explain current theories on how and when the boulder fields were formed. I was so excited to be in the mountains again I ended up being a bit early and while I waited for Thom I visited with the Ammonoosuc River for an hour. Even after the recent spate of rain the water level in the river had not risen dramatically.

Watching the Ammonsoosuc River churning through this gorge as it cuts a deeper and deeper channel through the bed rock is a reminder that water, in its myriad forms, is a key agent in sculpting the landscape as we see it today. Of course the sculpting has been going on for an unimaginable amount of time measured in millions of years, and it's not just water but the climate itself, the mix of moisture (as rain, snow, frost, and ice), temperature, and wind, that's responsible for the constant evolution of the landscape. What we see in the fractional moment is a mere snapshot, the blink of an eye, in terms of the continuum of change that's occurring around us however slowly.

Thom has been around the White Mountains as long as I have and has been at the fore front of local alpine and glacial geology for many of those years. As a college professor he's authored numerous papers and taken a lead in several ongoing discussions that, at times, become controversial, dealing with the complex nature of the geology and glaciology of the White Mountains. Thom speaks of these discussions as being friendly and collegial. One that he's been involved in for decades focuses on whether alpine glaciers occupied the glacial cirques in the Presidential Range after the Wisconsinan Glacial period. The accepted theory is that alpine glaciers predated the continental ice sheet. Thom's magnum opus is his extensive research of Mt. Katadin in Maine but the White Mountains occupy a lot of his time. He'll be working with geologist Brian Fowler on a new Map of The Surficial Geology of the Presidential Range that Brian collected a trove of data for this past summer. The mapping project is in collaboration with J. Dykstra Eusden, of Bates College, who recently published The Presidential Range: It's Geologic History and Plate Tectonics (2010) with its excellent fold-out map of the bedrock geology of the Presidential Range. The two maps, the surficial geology and the bedrock geology, will compliment each other.

(These new maps update R.P. Goldthwait's Geology of the Presidential Range (1940) and the Geology of the Mt. Washington Quadrangle published by M. P. Billings, et. al. (1946). Also in 1946, Billings and his cohorts collaborated with R.P Goldthwait on a booklet titled Geology of the Mt. Washington Quadrangle published by the New Hampshire Planning and Develolpment Commission. In 1951 Billing's published Geology of New Hampshire reprinted in 1962, 1968, and 1980, that was a companion to R.P. Goldthwait's 1951 publication: Surficial Geology of New Hampshire. A third companion volume published in 1951 covered the minerals of New Hampshire.)

On our hike Saturday I found that Thom possesses an encyclopedic knowledge of local geology and it was a great pleasure and educational experience to hike with him. Since we had a late start and the day was a bit dark with a thick mist settled low over the mountains on Thom's suggestion we decided to hike up Caps Ridge Trail to the summit of Jefferson to find some felsenmeer to poke around in instead of hiking up Mt. Washington.

This is Mt. Jefferson (5716') (in a photo from 8-29-10)(note the felsenmeer in the foreground). Caps Ridge Trail perches on that smooth incline slanting down on the right from the summit. The trail begins at 3,011 feet right off the Jefferson Notch Road (closed from mid-November until mid-May). This relatively high starting elevation shortens the hiking time up to the ridge. It's a rugged trail in places, offering some challenges particularly with winter conditions.

The smooth-looking incline of Caps Ridge in the photo shows the direction of the "continental" glacier, the "Wisconsinan", as it ground its way over and around the Presidential Ridge. The vast ice sheet traveled right to left in the photo, or northwest to southeast. The Great Gulf Wilderness is on the left in the photo, in the shadows.

A lovely, light snow was falling as we left the started up Caps Ridge. The trailhead is a little higher than the Base Station thus a small change in the weather. From the trailhead up to about 4,300 feet the Caps Ridge Trail crosses granite bedrock called "two mica granite", an igneous rock classified as "a light gray to white granite" found in several areas in the Mt.Washington quadrangle including a large area north of Pinkham Notch.

As we climbed Thom reminded me that felsenmeer occurs in all types of rock including granite, sandstone (in the Canadian Rockies), volcanic (the Olympic Mountains) and in metamorphic schists as in the Littleton Formation of the Presidential Range in the White Mountains. Different rock types react differently to the physical and chemical processes involved in the formation of felsenmeer but the key ingredient is climate. The climate responsible for the formation of the felsenmeer includes lots of water and daily (diurnal) or seasonal temperature fluctuations that cycle between freezing and thawing over relatively short periods of time. Since I kept referring to the ancient past in reference to the felsenmeer, Thom reminded me that iit's still going on today.

The forest between the Jefferson Notch Road and treeline on the Caps Ridge Trail shows the impact of perennial disturbances. The ridge portrudes northwesterly from the main ridge of the Presidential Range and is like a ships prow that's subjected to a continuum of intense storm activity and high winds. It also creates a venturi-like effect that increases air density and, with it, the speed of air masses climbing up over Mts. Jefferson and Clay.

In the freeze-thaw cycle, as the water melts and expands, it can exert a force of 22,000 pounds per square inch and in a paper on felsenmeer Thom that cited it stated a force that great easily fractures granite.

Frost plays a pivotal role in the formation of felsenmeer: first by prying apart (fracturing) jointed bedrock into rough blocks (boulders) and stones and, second, by heaving the blocks upwards from the bedrock several feet (1-2 meters) until they rest on the surface or on top of each other where they are evident today in the vast boulder fields called "felsenmeer" (German for "sea of rocks") on the higher summits and plateaus of the Presidential Range.

The mist and falling snow persisted as we climbed above treeline and across the first of several "Caps" which are massive protrusions of bed rock. The trail goes up straight over each of the caps which provides some novice rock climbing in a few places and some fine views of the ranges.

This massive "chunk" of mica schist, a member of the "Littleton Formation", looks intimidating in the mist and snow. In my youth, presented with this in my path, I would have eagerly climbed the rock, rather than hiking around it, pretending I was on a first winter ascent of the Eiger.

Initially the Littleton Formation consisted of thick sediments deposited on the floor of an ancient ocean where they were transformed into sedimentary rocks. Much later they were transformed into metamorphic rocks, in this case mica schists, under enormous pressure and heat, the result of continents, tectonic plates, shifting and colliding. The current theory holds that the White Mountains were formed during the Acadian Orogeny during the mid-Devonian epoch more than 400 million years ago. Eusden, using a computer model, determined that at the conclusion of the Acadian mountain building period the White Mountains were as high in altitude as the present day Rockies; around 15,000 feet (6 km) above sea level.

This large block of the Littleton mica schist is serving as a trail marker (the rectangle of yellow paint). Thom pointed out that the cracks are visible traces of the folding that occurred in the rock before it cooled. He added that the schist was "deformed" several times over the last 400 million years, the last time roughly 200 million years ago.

He also pointed out these stones sheltered under the block of schist a number of which are "glacial erratics".

After crossing over the last Cap, at about 4,500' we entered a large boulder "field". This is the felsenmeer and both the sizes and shapes of the rocks vary enormously. How the boulders get stacked and lie on top of each other, even huge blocks like the one in the foreground, is the feature of the felsenmeer that's captured my curiosity.

If you enlarge this photo on your computer you can see soil around the base of these boulders which is likely a relatively new soil consisting of "fines" (small particles) and pebbles created by the continual erosion of the larger boulders by "frost weathering".

At this point, the formation of the felsenmeer has been explained in rather simple terms, but, as Thom observed, it's a much more complex process involving interactions between the types of bedrock, the degree of slope, temperature gradients, available water, soil development, and the specialized environment in which this all takes place. I'll try to help you navigate through the beauty of these complex processes starting in a minute, but first there's some terminology that needs defining.

The mist was beginning to thin as we approached 5,000' and there was as blue tint in the sky behind Thom and there was a the feeling it was about to clear.

Two terms directly related to the felsenmeer include: "Quarternary" and "Periglacial". The Quarternary Period is a unit of geologic time comprising the last 2.6 million years. It is often referred to as the Quarternary Ice Age. It began with the beginning of the Pleistocene and the beginning of a cold, dry climate that produced the glaciation of the northern hemisphere. The Quarternary also covers the time that human civilization began to emerge. To refresh your memory the Quarternary is the present time period of the Holocene Epoch of the Cenozoic Era. The Holocene bring us to the present "interglacial period".

A minute or two later, with a little fanfare, the clouds rolled away to the south opening up vistas that continued to widen as we climbed.

"Periglacial" in one usage describes geomorhpic processes (e.g. the felsenmeer) occuring on the periphery or edges of glaciers and glacial areas. My attempt at a definition of Periglacial is as follows: An area not (necessarily) buried by glacial ice but subject to intense freeze-thaw cycles and that may have geomorphic processes occurring as the result of permafrost. On-line dictionaries and encylcopedias have more definitions that may, or may not, be useful.

Periglacial Processes and Environments (1973) by A. L. Washburn (Albert Lincoln Washburn and referred to simply as "Link") is considered the standard reference in the field today for studying periglacial processes. With Thom's help I was able to obtain a copy of Washburn's book from a small shop in Cornwall, UK. (The postage was more than the book price.) For the past few weeks I've been reading Washburn and a other papers on periglacial phenomenon from around the world that Thom forwarded to me and I've been enjoying this leap into an astonishing new world. I've discovered that my curiosity with felsenmeer is well deserved and that many of the questions I've had regarding its formation are shared by many others.

The clouds continued to peel away exposing the summit of Mt. Washington and a bit of Mt. Clay.

In his book, Washburn reports that the term Periglacial "was introduced by Lozinski (1909) to designate the climate and the climatically controlled features adjacent to the Pleistocene Ice Sheets (the large glaciers covering most of the northern hemisphere).
"It's been extended to designate nonglacial processes and features of cold climates regardless of age andof any proximity to glaciers. As a result there have been varying usages. Although not without criticism because of its lack of precision, the term is being widely used in the extended sense, as herre, because of its comprehensiveness.

The term has not generally recognized quantitative parameters, although some rough estimate of precipitation and temperature limits have been given. According to Peletier's (1950) estimate the periglacial morphogenetic region is characterized b an average annual temperature ranging from 5 degrees (F) to 30 degrees (F) (-15 C to -1(C)). Peletier quanitified annual rainfall (excluding snow) ranging from 5 inches to 55 inches (127 mm to 1397 mm). The diagnostic criterion is a climate characterized by significant frost action and snow-free ground for part of the year." (Washburn, pg. 1)
Frost action described by Washburn includes "Frost Wedging": "the prying apart of materials, commonly rock, by expansion of water upon freezing. It's synonymous with frost splitting and congelifraction. Frost wedging characteristically produces angular fragments that can be of widely varying sizes, ranging from huge, house-size blocks to fine particles" (58), as in the photo above and several others presented here. This felsenmeer is part of an extensive area beginning at 5,000 feet and that wraps around the Jefferson summit. Whether there is a distinct lower edge, or boundary, for the felsenmeer is often talked about by researchers. In the White Mountains the felsenmeer, generally, is confined to above 5,000 feet but that may be because of the slope which steepens below that altitude in many places.

Washburn writes at length about the subtle details regarding rock material, the environments, the climate including zonal climate, local climate and micro climate, time, and topography, etc. He writes of the interrelationship between these factors as "in periglacial environments, thawing of snow or ice adjacent to dark rocks warmed by insolation (the sun) is common at subfreezing air temperatures and must be a potent factor in frost wedging when meltwater seeps into joints and refreezes." (58). In another observation he says "The frequency of freeze thaw cycles is an important control in the effectiveness of various kinds of frost action, including forest wedging. However, the purely climatic factor of the number of times the air temperature passes through the freezing point is not, in itself, an adequate measure of the effectiveness. The insulating effect of snow and vegetation, the nature of the rock material, and the rapid attenuation of temperature fluctuations with depth must all be taken into account in evaluating the fequency and effectiveness of freeze-thaw cycles in rock materials." (58)

Well above treeline the trail takes the aspiring hiker over several false summits that, from above, looks like this. The desire to go higher for us was the desire to get above those clouds in the background and bask in the sun for a bit.

From studies in the Narvik Mountains of Norway, The Drakensberg Plateau of South Africa that Thom sent be papers on as well as Washburn's work in northern Greenland and arctic Canada, and Goldthwait's work in the White Mountains there's a lot of information about felsenmeer we can rely on. Here's a short list of things we definitely know: felsenmeers have an average depth of 39 inches (1 meter) although they're reported, in some studies, to be 70 inches (2 meters) in depth. They're found in high mountain periglacial environments (such as the area above 5,000 feet a.s.l. in New Hampshire's White Mountains) near or above the Arctic Circle, in Iceland, and other areas mentioned above. They are common in these regions, e.g felsenmeer is not unique to the White Mountains and Ragnar Dahl's prolific studies (1956-1966) of felsenmeer in the Narvik-Skjomen area of Norway indicates extreme similarities in the felsenmeer he studied and the felsenmeer found in the northern Presidential Peaks (Mts. Washington, Clay, Jefferson, Adams, Sam Adams, and Madison) of the White Mountains.

We also know that felsenmeers form on slopes of 25 degrees or less. (I'm accepting this until there's an opportunity to accurately measure degree of slope on the east side of the Mt. Washington summit cone.) A higher degree of slope results in the boulders being transported by gravity downslope. The existence of the felsenmeer and the processes involved in their formation all fall into the category of "mass wasting", and, one of my big questions, the age of the felsenmeer, is accepted by most researchers as relatively young. Most of those studies state that felsenmeers formed since the end of the last ice age 14,000 to 20,000 years ago.

Thom and others have tried dating the felsenmeer using cosmogenic derived data based on the exposure of the rocks to cosmic rays. That data has contained some flaws that make it difficult to form conclusions. At any rate, the question of precise age of the felsenmeer is still open although the figures presented seem reasonable and comparisons with other periglacial environments these processes might still active and on-going. Daily and monthly temperature gradients and mean temperatures for each of the 12 months of the year are available through the Mt. Washington Weather Observatory and indicate the potential for the occurence of periglacial processes during several months of the year including spring and fall. In Norway the micro climates in and around rocks and the amount of available moisture necessary for freeze-thaw cycles to occur were studied carefully over several years. The findings in those studies would most likely have a close "fit" to conditions here, in the White Mountains.

Questions that come up, at least for me, involve the position of some glacial erratics in the felsenmeer like the sub-angular boulder in the center of the photo that Thom pointed out just literally a few feet below the summit of Jefferson and...

this one located right at the summit. We assume that felsenmeer formed following glaciation and was not part of the glacial process so the presence of erratics in the boulder fields poses several questions regarding their transport there. R. Dahl (1966) quotes studies in which erratics were found in block fields that are "allochthonous" meaning from out of that area and possibly derived from glacial till deposited there. Other studies cited by Dahl considered the felsenmeer to be both "autochthonous" meaning locally derived and allochthonous. One report stated that, "it is not uncommon to find many erratics which are not frost-weathered in the block-field zone. If they are numerous, it is possible that the block field consists of glacial till." (R. Dahl, 58)

Looking at this photo of Jefferson's summit brings up one a nagging questions about the felsenmeer and how these large blocks got piled up on top of each other in this random assortment. An answer is provided by Washburn and his explanation of two more terms from the periglacial lexicon: Frost heaving and Frost Thrusting.

"Pressure generated by freezing water is exerted in all directions," Washburn wrote, "but they are expressed in soil movements only upwards and horizontally. The vertical expression is called heave and the horizontal, thrust.

"Blocks, frost wedged from bedrock, along joints, are raised (heaved) well above the general surface in places although the blocks are still tightly held by the surrounding bedrock." he added.
Photos in Periglacial Processes and Environments show huge blocks that have been heaved upwards and that are resting on other blocks in the same manner as evidenced on the summits of Mt. Monroe, Mt. Adams, and on Mt. Jefferson, where the summits themselves consist of felsenmeer. The obvious conclusion is that, as the felsenmeer is not of great depth and the bedrock is only a few feet below the random assortment of blocks, the individual blocks were frost heaved upwards in the manner described and at somewhat different times.

Another term, "upfreezing", describes the mechanical action of frost on pushing stones upwards to the surface. In 1973, at the time Washburn's book was published, "the mechanics of upfreezing is poorly known," the author wrote. He experimented with variations of this process by placing "targets"(e.g. wooden dowels) in the ground at varied depths and measured elapsed times for them to be pushed out of the ground. He and other researchers then developed what were called the "Frost-Push" hypothesis and the "Frost-Pull" hypothesis" both of which are variations of frost heaving but have importance in the periglacial process called "Patterned Ground" which is a well known phenomenon in the alpine areas of Mt. Washington.

The clouds seemed to settle down into the cooler area of the valley but then began to yo-yo around us and a higher level of clouds filtered the afternoon light making it cooler and making it feel later than it was. Odd pieces of Mt. Washington are showing through rents in the clouds to the extreme left.

Another question I have about the formation of the felsenmeer within the time line we have discussed is whether the boulder fields began to form after the culmination of the ice sheet and as it began melting back leaving the summits clear of ice little by little down to about 5,000 feet a.s.l. as in the photo above if you imagine that the clouds are the top of the ice sheet.

The reason for asking is that it might explain several things. One is that the melting ice would have provided the ample water needed for frost wedging of the bedrock as well as the ambient temperatures close to those proscribed by Washburn and others as optimal for periglacial processes including frost wedging/weathering to occur.

Thom's response to my questions about timing and time lines is that almost all of the periglacial processes we've been exploring occurred concomitantly (in the same time period) as the ice sheet dissolved.

In this zone on the south slope of the Mt. Jefferson 300 feet below the summit the slope eases and we find soil that has collected here from the mass wasting of materials from the boulder fields higher up on the mountain. The soil is periglacial in origin and in its more primitive state would have been mostly fines and gravels from the frost weathering process but once vegetation is supported an O horizon develops as in the photo.

This photo shows the bedrock to the right and gelifluction (a form of "mass wasting") occurring in the movement of the soil, to the left in the photo, down slope. Terms for mass wasting described by Washburn include avalanche, slushflow, slumping, frost creep, rock glaciers, and gelifluction. Gelifluction, similar to solifluction, is the slow downward flowing of waste saturated with water over frozen ground. Solifluction is the same process but not restricted to cold climates or frozen ground. Washburn states that "Gelifluction is unequivocally periglacial." (173). His insightful research into frost heaving and mass wasting opened up a window on myriad kinds of vertical movements caused by frost action but also lateral movements and combination of the vertical and lateral movements such as "mass displacement" and "frost cracking".

Mass wasting may have been the origin of the larger, nearly level areas of vegetation on the Presidential ridge, what are referred to as "lawns'. These lawns on the Presidential Range were referred to by Goldthwait and others as remnants of the New England Peneplain, an ancient erosional surface left over from pre-glacial epochs. The lawn in this photo is a segment of what is descriptively called Monticello Lawn as it's located on Mt. Jefferson. Monticello Lawn consists of many acres and curves around the southeast side of the Mt. Jefferson summit cone at around 5,000' a.s.l. Parts of Monticello Lawn contain "hummocks" and "steps" which are features of periglacial environments and the lawns, themselves, are likely the result of periglacial processes such as mass wasting as mentioned above, as are smaller grassy areas (smaller lawns), referred to by Goldthwait as "grass cells" that are conspicuous in the area above treeline. I've often thought about doing a research project focusing on these "cells" to better understand their origin, micro climate, expansion and/or contraction, and their ecological significance.

A last thought about Monticello Lawn is a memory of a distant summer when some overly ambitious (exhuberant?) hut croo set up a croquet game complete with stakes and wickets, colorful croquet balls and a couple of mallets leaning on a well anchored lawn chair on which a Sunday edition of the New York Times was also anchored (from the wind) to look like someone had been playing a game of croquet and just left--all for the amusement of passing hikers.

This Bigelow sedge shows the raking force of the wind as it moves from the northwest around the summit and across the lawn. I've been here on winter trips when the only way across was to crawl because the wind was so violent. Washburn makes several observations about the contribution wind makes to the periglacial environment including the creation of dunes and sculpted rocks called ventifacts. The intensity of the wind that blasts the Presidential Range is world famous and impacts the periglacial environment by inhibiting vegetation growth above 5,000' a.s.l. and it may sculpt rocks and landforms as well.

Looking back up to Jefferson's summit as we begin descending back down into the clouds.

Washburn's explorations of vertical and horizontal frost action in periglacial environments has increased understanding of other periglacial processes like "frost sorting" which produces small and large stone stripes, stone polygons and large and small stone circles that are found on nearly level ground or on slopes of 3 degrees or less like the lawns around Mt. Jefferson, and Bigelow Lawn. If Thom and I had been carrying a tall step ladder we could have taken a photo from the top of it looking straight down on these rocks in the foreground to show they've been frost-sorted to into large stone polygons with Bigelow sedge in the cell-like centers.

In the past year we looked at block nets and block lobes (on Mt. J. Q. Adams), block streams and what might be a rock glacier on the Kings Ravine headwall all of which are associated with the periglacial processes of "creep". We've also looked at sorted and unsorted stone stripes and stone polygons on Bigelow Lawn on Mt. Washington's east side just north of the junction of the Davis Path and Camel Trail that rival those photographed by Washburn in Greenland and Arctic Canada.

Time to head down.

Winter's approaching.

This is the western edge of the lawn. To the left the slope drops steeply towards the valley. The gentle slope of the lawn is important as it defines the limits of vegetation here as well. From here we descended back down into the mist and light snow that was still falling. It was unique to hike down the mountain and into a snowstorm.


Andrew Riely said...

The eleventh picture from the bottom, of Washington rising above a layer of cloud, is a pretty good model for what the Presidentials would have looked like if they were indeed covered up to their summit cones by a glacier during the last ice age.
Enjoying the posts!

Alex MacPhail said...

Hey Andrew! You missed the reunion the other night! We missed you. Ari was there and I finally met him in person. Hope you're healthy and happy!