Great Range - Wikipedia style...

[bubba]

I just found this on Wiki and wonder if others agree. I'm stumped.

"The Great Range is a mountain range in the the Adirondack Mountains, near Keene Valley, New York, USA. It rises in the heart of the High Peaks region between Ausable Lakes to the southeast and the Johns Brook Valley to the northwest.

The range is approximately twelve miles long and includes fifteen of the forty-six High Peaks. They are, along the main ridge from northeast to southwest, Lower Wolfjaw, Upper Wolfjaw, Armstrong, Gothics, Saddleback, Basin, Marcy, Skylight, Redfield, and Cliff, and on a southern spur, Allen.

Sawteeth is a spur of Gothics, Haystack is a southern spur between Basin and Marcy, Colden is on a spur west of Little Marcy, and Gray is a spur due west of Marcy."

To start with... I always thought Marcy was optional - whether you included it or not. But then... adding Skylight, Redfield and Cliff?? And Haystack as a spur?? Never seen anything like it!

 

[Tom Rankin]

I just found this on Wiki and wonder if others agree. I'm stumped.

to start with... I always thought Marcy was optional - whether you included it or not. But then... adding Skylight, Redfield and Cliff?? And Haystack as a spur?? Never seen anything like it!

So edit it to fit your version of reality!

 

[Kevin Rooney]

I'm no geologist, but I don't think it's a mountain range. Hasn't the term been used to describe a long day hike, much like a Presidential Traverse in the Whites?

 

[bubba]

So edit it to fit your version of reality!

Funny boy! I was trying to see what others thought was reality!!

Kevin - I'm pretty sure that the term "range" is appropriate. It's called the Great Range. Next over is the McIntrye Range...

 

[Mark Schaefer]

There are no generally or universally agreed to definitions of what a mountain range is, either from a geological or geographical perspective. If you click on the Discussion tab of the Wikipedia Great Range article you will see the admission: "the article needs more work!".

On the Peakbagger website, a hierarchy of ranges is used. There are different numbers of levels in different parts of the world the world. The world is defined as level 0, each continent is level 1, etc.

In their classification the Adirondack Mountains are a level 4 range. Within the Adirondack High Peaks, level 5, are the Great Range and Marcy Group at level 6.

Their definition is perhaps close to the common usage of the Great Range. However, they include both Marcy and Haystack within the Marcy Group. I believe that is because the Marcy-Haystack col is higher than the Haystack-Basin col. One could define a range at the lowest level in terms of the line of highest summits along a ridge, or in terms of the lower cols which separate the parts of the ridge.

The Peakbagger classifications and Great Range definition seem reasonable to me. But that is just one man's opinion.

 

[--M.]

I know I could find this elsewhere, but why not hear it from a hiking geologist?

What accounts for the northeast/southwest orientation of the DAKs?

Is Indian Lake dammed? Was it there before the dam? Would Lower AuSable Lake be more than a trickle without its dam? Is there a dam on the upper lake (haven't been there yet)?

As to the original post, I would agree that Marcy, the Haystacks, Skylight and Redfield are approximately involved. I'd draw the line at Cliff. But doesn't this beg the question of the difference between opinion and expertise? I admit I'm just a guy with a map.

 

[Puma concolor]

Summit Post has a good page on the Great Range and tries to address some questions as to what peaks should be included.

Great Range

 

[Mark Schaefer]

What accounts for the northeast/southwest orientation of the DAKs?

I am not a geologist, but I will take a non-technical stab at this from my readings on the subject.

The rocks of that were to become Adirondacks were formed during the Greenville orogeny which took place in 1.12 billion years ago. The Proto-North America continent collided with the Grenville subcontinent. The alignment of the collision front was basically along the current northeast-southwest line. As the pressure increased fold and stress lines were created along lines perpendicular to the direction of impact and parallel to the collision front. About 600-650 million years ago the Greenville rocks were stretched as the pressure was relieved creating the northeast-southwest fault lines along the former stress lines in these rocks.

The actual rise in the Adirondacks dome/bubble is far more recent, 10-20 million years ago. At the start the old Greenville rocks were buried under hundreds of million years of more recent sedimentary rocks. Those sedimentary rocks have eroded away as the basement Greenville rocks and their fault lines were exposed. Lakes and streams formed in these fault lines. During the ice ages temporary blockages were created, stream flows sometimes reversed, occasionally streams were captured across the fault lines.

Is Indian Lake dammed? Was it there before the dam? Would Lower AuSable Lake be more than a trickle without its dam? Is there a dam on the upper lake (haven't been there yet)?

Many of the fault line lakes in the Adirondacks have had their levels raised by manmade dams, but in virtually all cases the depths of those lakes are much lower than the dam bases, and so they existed prior to the dams. The Lower Ausable Lake was definitely there prior to the dam. I do not know whether there is a dam at the Upper Ausable Lake, but it is likely. Indian Lake has a dam, and the lake existed before the dam.

Those same basic northeast-southwest Greenville fault line alignments have also determined the eastern front of the Catskill mountains known as the Wall of Manitou, as well as the Delaware, Neversink, Basher-Rondout valleys. In the case of the Catskills the Greenville rocks and fault lines are still buried under several thousand feet of Queenston and Catskill sandstone, but the sandstone has cracked along and above those underlying fault lines as the sandstone layers were uplifted intact. The sandstone above those cracks eroded faster leading to the formation of the valleys. During the ice ages temporary blockages were created, stream flows reversed, and some streams were captured across the fault lines -- similar to the Adirondacks.

 

[Mark Schaefer]

Summit Post has a good page on the Great Range and tries to address some questions as to what peaks should be included.

Great Range

Thanks for posting that link (created by a VFTT member). It basically agrees with the Peakbagger definitions, differing only in that the Peakbagger classification separates the Marcy Group off from the Great Range.

 

[Willie]

I know I could find this elsewhere, but why not hear it from a hiking geologist?

What accounts for the northeast/southwest orientation of the DAKs?

My credentials: M.S. in Geology (thesis: A structural geometry of the northern terminus of the North Mountain Thrust Sheet, Southcentral, Pennsylvania).

As stated previously, the exposed basement that comprises the Adirondack High Peaks is Proterozoic in age (about 1.3 - 1.0 billion years old). However, the northeast/southwest striking normal-sense, brittle faults, which may be a reactivation of Greenvillian age ductile shear zones, are late-Mesozoic in age (about 100 - 150 million years old) and have been related to the uplifting of the Adirondacks. It is thought that the Adirondacks began to uplift in the Mesozoic, and that uplift continues today. It has been suggested that the uplifting is caused by: (1) a hotspot beneath the Adirondacks which uplifts by buoyancy; (2) thermal expansion of the lithosphere, or (3) isostatic rebound following deglaciation.

 

[--M.]

Fabulous stuff, and pretty much what I expected to see. So now, let's get working on what drives a range to configure itself the way it does, and why Gothics, Armstrong, the Wolf Jaws, etc. are in a line, while Haystack and others are offset. Any informed (and not-so-) opinions on what drives the original poster's observations on what actually comprises the "Great Range"?

Geologically speaking, did these peaks emerge simultaneously, or in a line (as if a hot spot in a lower plate were passing under a fixed point), or what? Can one create an animation of a timeline showing the emergence of each of the 46? "Look, here comes Whiteface. And next up is Santanoni/Panther/Couchie." Could it work this way? Why did Algonquin end up where it is?

Thanks for these great entries, Puma concolor, Mark Schaefer and Willie!

 

[ALGonquin Bob]

My maverick spurs go "jingle-jangle-jingle"...

 

[Willie]

So now, let's get working on what drives a range to configure itself the way it does, and why Gothics, Armstrong, the Wolf Jaws, etc. are in a line, while Haystack and others are offset. Any informed (and not-so-) opinions on what drives the original poster's observations on what actually comprises the "Great Range"?

Geologically speaking, did these peaks emerge simultaneously, or in a line (as if a hot spot in a lower plate were passing under a fixed point), or what? Can one create an animation of a timeline showing the emergence of each of the 46? "Look, here comes Whiteface. And next up is Santanoni/Panther/Couchie." Could it work this way? Why did Algonquin end up where it is?

There are problems with the Adirondack hot spot hypothesis, and, unlike the Hawaiian hot spot that created the individual mountains of the Hawaiian chain, and unlike the Yellowstone hot spot that left a trace through the Snake River Plain, I am unaware of any evidence that the Adirondack mountains formed, individually, as the lithosphere passed over hot spot. A better explanation seems to be that the Adirondacks were uplifted contemporaneously. Brittle faulting during uplift, throughout the High Peaks, created a condition that allowed differential erosion to occur (i.e. crushed rocks in fault zones were eroded faster than solid rock not in fault zones).

The Adirondack Mountains comprise a single physiographic province. The individual mountains within the Adirondacks, as discussed above, are separated by eroded fault zones. So the identification and naming of “mountain ranges” is really a matter of scale and a determination of which fault blocks you include or exclude from any particular mountain range. For example, a major fault zone passes through Panther Gorge and proceeds through Johns Brook valley. So, in my mind, the "Great Range" is the fault block bounded by Johns Brook, Panther Gorge, the Ausable Lakes, Ausable River/Keene Valley. In another example, a fault zone trends NE from Slide Brook to South Fork Boquet River, which separates Macaomb, Carson and Grace from Hough and Dix. But, the five Dixes have historically been considered to be single "mountain range."

 

[eddie]

So Willie, what your saying is that what looks like a range in the eye of the beholder is a range. And I'm OK with that.

 

[moonrock]

Here's my version/encapsulation - others feel free to update/correct the science
(Geology MS, Rensselaer 1984).

In the GRENVILLE orogeny, 1200 MYA, eastern North America crunched into "Amazonia" – now part of South America. The Grenville mountains were likely Himalayan in size/area; their remnant or “basement” rock extends from present-day Greenland to Georgia (US), sometimes at great depth. In the High Peaks region, the bedrock beneath the original mountains was intruded by batholiths (blobs, tens of miles wide) of hot liquid anorthosite, which solidified in place miles beneath the surface.

By the time the supercontinent split apart (~700 MYA), the Grenvilles had probably eroded down to a regional plateau. As the continent broke up, the crust along the broken edges stretched, faulted and subsided. Sea levels increased several hundred feet worldwide, inundating large continental areas. As a result, the subsiding Grenville rock throughout NY State was gradually covered by thousands of feet of marine limestone, sandstone and shale.

Around 400-250 MYA, a new series of collisions (including, finally, with Africa) formed the Appalachians (the latter include some Grenville rock, thrust back up to the surface by faults). But the Adirondack mountains did not appear until much later, as the region separately domed up, and the overlying marine rocks broke up and eroded away (like slicing the top ¼ off an onion). At some point the exposed Grenville basement eroded enough to expose the anorthosite “core” (like the pulp of a badly worn molar tooth). The anorthosite was harder to erode away than the capping (or surrounding) rocks and so ultimately formed many of the High Peaks. But it is estimated that an 18-mile thickness of bedrock was removed to expose the current high peaks summits – that’s about 3 times the cruising altitude of a passenger jet !

A hot spot is not needed to produce moderate uplift and erosion at old mountain ranges. One hypothesis is that forming ranges initially project “keels” of continental rock deep into the denser material below. That contrast in density later tends to “rejuvenate” worn- down ranges, buoying up the old rock, even as surface erosion strips it away (like unloading a barge). The original, Andean-height Appalachians also were eroded nearly flat, but were “rejuvenated" to their present heights, possibly in the same way. The Adirondack uplift may be due to a hot spot, but the lack of associated volcanism (think Yellowstone) is suspicious, and other explanations account for the Saratoga springs.

As for where INDIVIDUAL high peaks form, remember that the present-day mountains were ERODED into being. Erosion along the major fault valleys defined the ranges. But the faults are neither vertical nor perfectly linear. And between them, bedrock is also fractured, but fracture orientation and spacing varies, as does rock chemistry and resistance to chemical erosion. In addition some of the bedrock has a directional metamorphic “grain” which also controls its fracturing. And smaller igneous intrusions can affect the erosion and resulting topography.

So the complex interplay of lithology, fractures, erosion and drainage prevented the formation of a perfect, geometric array of mountain ranges, peaks and valleys.
Hope that's not vague.

MR

 

[MattC]

Thanks to all for the posts, especially the geologists. I had heard of the "hot spot" hypothesis, but not the "keel."

I have a question that pertains not to the formation of the mountains, but to the rocks themselves. What are they mostly composed of, in terms of minerals, and what are those thick "veins" one sometimes sees cutting across open slabs? IIRC, some upper slabs on the trail up Giant from 73 is a place where they can be seen, but they are fairly common throughout the Adirondacks. They sometimes make good foot placements when crossing a slab.

Apologies to Bubba if my questions are too off the original topic. It's just cool that we have the attention of hiking geologists here.

Matt

 

[bubba]

...Apologies to Bubba if my questions are too off the original topic. It's just cool that we have the attention of hiking geologists here.

Matt

Matt - I'm totally blown away with the direction that this thread took!! Once again - this board provides the most expansive knowledge-base that one could imagine. Added to that is that our community seems to enjoy sharing information with others in such an friendly and non-confrontational way.

My original post concerned the inclusion of other mtns in the Great Range that I had never considered. I always thought the "Range" was Haystack to LWJ, and it was optional whether you included Marcy. When Wiki included all the others - my eyes/ears got opened a bit and I decided to post. Appreciate the input about the ability to change Wiki - I'd forgot that one could do that... and my interest was in opening up the post to what others considered the Great Range rather than correcting what Wiki had to say (although maybe we should agree to what should be said and one of us make the changes).

With regard to your question about the composition of the ADK's - the one thing that I do recall is the Whiteface and Esther are different kinds of mtns than the rest of the HPs. (I bet that get's a comment - and hope it does cause I don't recall the specifics.)

Thanks to all for the informative and fun posts. Hope others find it.

 

[Willie]

[W]hat your saying is that what looks like a range in the eye of the beholder is a range.

Yes, eddie, that’s the underlying premise. I believe it’s human nature to separate “mountain ranges” by deep valleys. For example, the MacIntyre Range is separated from other ranges by well-defined, deep valleys. However, other mountain ranges, such as the Wilmington Range and the Stephenson Range, are separated from each other by a less well-defined valley, which raises a question: Is Morgan a part of the Wilmington Range or the Stephenson Range? Now, going back to one of the original questions: Is Marcy a part of the Great Range? Why or why not? We should ask the person who originally named the various mountain ranges why he or she included or excluded certain mountains. Unfortunately, however, I think the original namers are long dead, but I imagine that there’s a historical record.

 

[moonrock]

The central high peak anorthosite is the same rock class that makes up the majority (bright area) of the moon's crust. Other types of igneous and metamorphic rock (like granite and gneiss) are also present, but anorthosite (technically anorthosite gneiss, since it has since been squeezed and re-heated a bit) and "gabbroic anorthosite" account for most of the summits.

Anorthosite consists primarily of a type of feldspar rich in calcium, midway in compositional range between CaAl2Si208 and NaALSi308. It formed back in Precambrian times, deep in the crust near the mantle. As a deep magma body starts to cool, specific mineral types crystallize first, specifically iron-magnesium rich silicates (olivine, pyroxenes) and calcium-rich feldspar, gradually depleting the liquid of those elements. If the FeMg minerals settle out, and the remaining liquid remains mobile, the liquid and growing feldspar crystals can migrate elsewhere (upwards) and form other rocks (like anorthosite), which are very different from the original magma composition.

The Adk anorthosite apparently formed in two stages and distinct textures: a coarser rock containing (settled-out) large crystals of calcium-rich feldspar (labradorite), and a finer grained rock that formed at shallower depth. In outcrops of the former, labradorite is visible as thumb-sized blueish crystals embedded in a finer-grained white, gray or greenish matrix. The crystals are "twinned" - divided lengthwise in their molecular patterns - so when you look at them from different angles, one or the other half may "wink" at you as it catches and refracts light.

In places faulting thrust giant, solid slabs of the coarser crystalline anorthosite up from depth to overlie the finer rock. An example is Big Slide: the top of the peak is a resistant remnant of the overthrust, which "capped" the underlying rock as Johns Brook Valley formed. The profile of the mountain is assymetrical because of the low angle (upwards north-to-south) of the fault, which vertically separates the two.

The massif is also split and intruded by dikes of darker (mafic) Fe/Mg-rich rock similar to gabbro (basalt formed underground). Colden Dike is a large mafic igneous intrusion into the rock mass that later eroded to form Colden.
The dike rock fractured in a distinct pattern as it solidified and contracted, which is one reason for its step-like profile. The fracturing (combined with its lesser resistance to chemical weathering) helped it erode to the incised cleft we see today.

Other lighter veins you might see could be quartz, though I don't know how prevalent it would be around anorthosite. Quartz veins are common near granite bodies, because they are more silica rich, and silica is one of the last things to solidify and one of the first to re-mobilize when reheated

Surrounding the igneous/meta-igneous central adirondacks are intricately folded belts of metamorphic rock including gneiss, schist, and marble. Minerals that can be found there include (among others) garnet and even graphite. The mines near Newcomb were there because of Ilmenite, an uncommonly titanium-rich mineral that also separates (settling out in this case) as certain magmas cool and differentiate.

Dikes and various rock/mineral exposures are especially visible along several rock cuts along the Northway, but even geologists get hassled if they stop there.
"Back off, man, I'm a Scientist !" will get you three hots and a cot. And maybe a new address.

A lot of the above can be read in the paperback: Geology of the Adirondack High Peaks Region , which I highly recommend. It gives great (and hopefully contemporary) explanations of the history and geologic processes.

MR

 

[Willie]

[W]hat are those thick "veins" one sometimes sees cutting across open slabs? IIRC, some upper slabs on the trail up Giant from 73 is a place where they can be seen, but they are fairly common throughout the Adirondacks. They sometimes make good foot placements when crossing a slab.

I'm familiar with the veins on Giant. The veins are comprised of plagioclase feldspar megacrysts. Those veins were formed when hydrothermal fluids dissolved plagioclase from surrounding anorthosite and precipitated the plagioclase in fractures.