How Glaciers Sculpted the Sierras

Let us try and partially recreate the glacial events that may have helped to create the topography of Eastern Sierras. First the huge granite batholith was created underground in a series of island arc dockings. It was finished about 80 million years ago. Then about 3 million years ago the granite block began to rise. Since then there have been over 20 Ice Ages. The last one ended 10 thousand years ago.

During the Ice Ages, because of thick snowfall and cool summers, glaciers formed atop the crevasses of the mountains and then flowed along the river valleys, creating huge U-shaped basins. Judging by the walls it left behind, our glacier river, which scoured the granite block of the Western Sierras, was up to 700 meters Å 2300 feet thick, almost half a mile thick. When it was retreating it was much thinner as evidenced by the lateral moraine that was left some 200 meters above the base. It doesnÕt show on the topo map but must be there because of the two small lakes that were left and contained precariously on the side of the mountain.

The snow kept falling and the summers werenÕt warm enough to melt the ice. The glacier couldnÕt move the ice down fast enough and so grew taller than the tallest mountain, merging with other glaciers lower down to form an enormous ice sheet over the entire High Sierras. While the surface of the Sierras encompasses 25,000 square miles, the ice sheet was not connected to the huge northern ice sheets, which covered millions of square miles.

The glaciers didnÕt make it down into the lower lying Owens Valley to the east because of the steepness and the rain-shadow effect. Looking at our relief map the V-shaped valleys start almost immediately below Onion Valley at 2800 meters Å 9200 feet. On visual inspection, there is a distinct ledge here. It would seem that Onion Valley marked the furthest most advance of the Ice Age Glacier.

Meadow formation

Where is the lake that glaciers leave behind? Because of its low-lying status it has been turned into a meadow. Glaciers leave lakes. These lakes accumulate sediment on their bottoms. This sediment supports plant life. The plant life decays, creating soil which in the lower lying areas supports bushes. These bushes create more vegetal debris, which create more soil, which supports larger plants and smaller trees. This vegetation in turn continues to drop organic debris which fills up the glacier lake. Finally a forest grows in the deeper soil, choking out the larger plants and completely covering over the lake.

This mechanism is a common glacier phenomenon. First the glacier scours the ground, then retreats, leaving debris that will support plant growth. Additionally the glacierÕs meltwater rushes down the hill from the melting glacier, organizing the debris so that it will more easily support plant life. The first small plant life provides the soil for larger and larger plant life which supplants the smaller. Finally trees can grow on the thicker soil provided by the larger plants and supplanting them simultaneously.

Although glaciers scour the countryside they also provide the means of rejuvenation once theyÕve left. Hence Ice Ages are the way that the Earth cleanses and rejuvenates itself. It is like the severe pruning of rose bushes in the winter in order to create a healthier plant. In a similar way a economic depression clears out deadwood businesses, paving the way for a healthier economy. Ice Ages while destroying many forms of flora and fauna also set the stage for their regeneration upon their departure. This is a good example of a dynamic ecosystem, which is constantly evolving. This is contrasted with a static ecosystem where all the living things are in relative harmony. Many ecosystems are locally static and globally dynamic.

Parallel Lakes at Equivalent Altitudes

After depositing its terminal moraine our glacier retreats 800 feet up the side of the Eastern Sierras, stopping briefly at the location of Little Pothole Lake at 3060 meters Å 10,000 feet. It laid down another end moraine, which because of the outwash from the melt-water is covered with soil. (This is the ridge we hiked to that I thought was the top.) Additionally the glacier drops some of its ice. This along with the melt-water held by the end moraine forms Little Pothole Lake. The deep vegetation and the overgrown appearance of this lake indicate that in a certain amount of time that the lake will disappear replaced by a meadow and forest.

In the declining Ice Age the glacier then retreats another 300 feet up the side of the mountain to Gilbert Lake in the east and Charlotte Lake in the west both at 3170 meters Å 10,300 feet. It drops more debris to form rocky ridges to hold in both lakes. This end moraine is pure till, erratically shaped and erratically organized boulders with no sediment on top. (Hiking up to this ledge, we thought that we had reached the Nome KingÕs kingdom because of all the rocks.) Because of the shallow grade in the western Sierras, Lake Charlotte is 4 or 5 times larger than Gilbert Lake.

Again the glacier retreats another few hundred feet up the hill before pausing at Flower Lake 3210 meters, Matlock Lake 3218 meters, and Robinson Lake 3210 meters on the east and Bullfrog Lake 3234 meters on the west. Additionally on the west we have the enormous Rae Lakes at 3213. The Glacier must have paused here for quite awhile because of the size and number of the lakes. Again Bullfrog Lake and Rae Lakes in the west are substantially larger than the others because of the shallower slope. Again the melting glacier left till to contain the lakes and meltwater to form the lakes, maybe dropping off some chunks of ice to seal the bargain.

The parallel altitudes of the lakes is striking. These lake formations at nearly the exact location is not coincidental. The glacier retreat seemed to be punctuated by regular pauses. At each of these pauses lakes were left behind. The glacial retreat was in no way continuous. This glacier pulse finds parallels in drought cycles, growth spurts, chaos theory, quantum theory and the pulse of life.

(When making the relief map this parallel aspect of the lakes altitudes startled me. Being a southern California boy with no experience with glacier formations and being a theorizer par excellence, I thought that the incredible number of lakes at the same altitude perhaps had something to do with some odd mechanism between air pressure and the snow. Thinking simultaneous glacier retreat, the simplicity overwhelmed the complexity of the other theory, whatever validity it might have had.)

There is an incredibly sharp rise from the Matlock Lake system almost 1000 meters Å 3,200 feet. Here this part of the glacier had its last stand. There are no end moraines to hold in any lakes, just a steady deposit of till. The glacier death was a downloading of whatever it had left. A teacher retiring. ŌMy children these are some final words to remember me by.Ķ

(This moraine was incredibly hard to hike over. Though not dangerous, it was so irregular as to prohibit any steady progress. Additionally the granite boulders that made up the moraine are incredibly rough on the hands. Finally there was still snow on the sides of the mountain, even though it was a hot summerÕs day. Perhaps Dense glacier remains that are holding onto the rock?)

There is a medial moraine between Flower Lake and Matlock Lake in the east. (When hiking over it to Matlock Lake, I was tricked into thinking that I was in water based erosional valley because of the gentle grade and rounded hill. I was so convinced that when I was making the relief map I was shocked to find this hill only a divide that separated the two lake systems. Upon hiking, my false notion of mountain was confirmed. Upon construction, my notion was shattered - again.) Evidently the retreating glacier divided into two at this point, depositing till in this medial moraine as it divided. It then cleansed and organized it for plant growth with the melt-water. On the hill are some close relatives to the Bristle Cone Pine trees, the oldest living things on earth, sometimes up to 7,000 years old.

Our glacier melts another 300 feet up the hill to the 3300 meter level. Now we are approaching 11,000 feet. The sides of the mountain are exceedingly sharp. The melt-water from the glacier hollows out more lakes, which are contained by the deposit of more till dropped by the pausing glacier. We have lakes on the eastern and western side of the Sierras at this altitude. Again the lakes on the western side are much larger because of the shallower slope. Heart Lake, Bench Lake, and Parker Lakes are on the east while the much larger Kearsarge Lake system and Dragon Lake are the terraced lakes on the east. Each of these lakes rises in step fashion from a lake before.

Another 100 meter rise to about 3470 meters Å 11,400 feet, and on the east we have a 5 separate kettle lakes, at nearly the same altitude, within 10 meters of each other. The glacier is dropping the last of its ice to form these round lakes. The surface of the Big Pothole hole is at 3460. Three lakes separated by medial moraines in the Golden Trout Lakes system are all between 3460 and 3480 meters. Then there is one unnamed lake above Bench Lake to the south, which also falls in this same altitude.

(Arriving at Big Pothole Lake was startling because of the enormous basin that the Lake resided in. The surface of the lake was nearly 40 meters Å 120 feet below the top of the basin. The sides were sheer solid granite, no rubble here. It had all been washed down the hill. I had fantasized on the way up of going down to Big Pothole. The sides were far too sheer for a timid soul like me to negotiate. It seemed as if only someone with rock climbing gear could climb out, the sides were so steep.)

From Big Pothole it is another 130 meter rise to Kearsarge Pass at 3600 meters Å 11,800 feet. This is the lowest spot for a few miles in either direction on the north-south ridge that divides the eastern and western Sierra. It is the top of the trap door that was pushed up. The Glacier was on top of it all, eroding both sides with its enormous weight. Kearsarge Pass was a section where it broke through. As a shallow section it probably contained the last of the Glacier as it moved up and away. How sad. As an artist the Glacier sculpted the earth in incredible ways. Now it dies, leaving only the remains of its work. Nothing is left of its body except that which has been recycled into the earthÕs water system. But what remains!

The Medial Morraines of an Ancient Glacier

Glaciers tend to follow pre-formed V-shaped river valleys in their growth pattern, turning them into U-shaped glacier valleys. When the glacier retreats into these same valleys they leave behind their characteristic chain lakes, the paternosters. When the glacier splits up on the way back up the mountain, it leaves a medial moraine of sifted and unsifted drift, depending on whether it was ice dropping the drift or meltwater. I pointed out a small medial moraine between Gilbert and Matlock Lakes where we were camping. Wherever however that the glacier split into two it created these medial moraines, some small, some enormous. The difference between an arte and a medial moraine is that an arte is the sculpted rock that remains while the medial moraine is deposition from the retreating glacier. Ironically the glacier tears down the mountain walls between valleys on its way down the mountain side and builds them back again on the way back up.

There is a medial moraine between each of the lakes, which exist at the same altitude. There is an enormous medial moraine, which peaks at 3656 meters Å 12,000 feet, which separates the section of the Glacier that followed the Big Pothole path over Kearsarge Pass from the Glacier that followed the path of the Golden Trout Lake system. There are smaller medial moraines, which separate the Lakes in the Golden Trout system from each other.

One feature of these medial moraines is caused by the conveyor belt system of deposition. When the glacier pauses it drops a substantial amount of its till at the front, causing ridges to contain lakes in the main flow of the glacier and causing peaks at the front of the medial moraine. Some have compared this to the back of a whale.

We see this jutting peak everywhere in our small slice of the Sierras. In addition to many smaller jutting unnamed peaks that we have mentioned there are two enormous named peaks: Independence Peak at 3579 and Kearsarge Peak, itself at 3846 feet Å 12,600 feet. As mentioned these ridges are more rounded, similar to river valleys, but they consist of a mountain of granite rubble. They also have the characteristic whale back shape.

Surprise of surprises Mount Gould also has whale back shape. And just when I thought I was beginning to understand mountains. A friend of mine hiked relatively easily to the top of Mount Gould - no mountain gear, just by scrambling up the rubble. Rubble, whale back shape. Mount Gould itself is probably a medial moraine, rubble dropped by a retreating glacier. Mount Gould is a mountain made up of glacial debris that sits on top of a mountain range made up of solid granite. This is an example of the mountain peak being of a different nature than the mountain range that it is part of. WeÕll see this phenomenon again when we speak of volcanoes.

An enormous glacier of a prior Ice Age

The glacier, which deposited these peaks and mountains, transcends in size anything weÕve spoken about so far. The glaciers that formed the medial moraine of Kearsarge Peak and Mount Gould must have been enormous and of an earlier Ice Age. This is stated only because of the V-shaped valleys that commence at about the level of Onion Valley. The Glacier at this level must have been 1200 meters Å 4000 feet thick. The medial moraines of Kearsarge Peak and Independence Peak extend a few thousand feet past Onion Valley. One gets this sense of a huge glacier dropping its enormous moraines at an earlier time. This was followed by an interglacial where erosional valleys were reformed based upon running water. Then another smaller Ice Age occurred which wasnÕt as deep nor did it extend as far down but followed the routes of the larger Ice Age further refining the erosion.

The enormous ancient glacier theory is augmented by the multitude of large boulders scattered erratically around the base of the mountains near Independence at about 4000 feet. These boulders did not just roll down the hill. They are classic erratics deposited by glaciers.

If these peaks were medial moraines then where was the end moraine or more specifically the terminal moraine? Surprise of surprises, there is a 400 meter Å 1300 feet out growth of mountain which covers Onion Valley like a closed hand. (Upon driving up to Onion Valley, I was wondering where the opening was to the mountain because all I could see was a steep upgrade in front of me. Instead we drove around this projection and up the valley that Independence Creek follows.) It seems that when the Great Glacier retreated it left these medial moraines with the enormous terminal moraine in front. Then in the interglacial to follow and perhaps even the melt-water from the Great Glacier, eroded a pathway in the terminal moraine, which became Independence CreekÕs bed and then eventually the shortcut route for a car up to the High Sierras.

It seems that at least two distinct glacier phases are indicated. The most recent glaciation has left U-shaped valleys with just a very tiny V at the base, if at all. The evidence of the earlier glaciation is obscured by the later higher up. However below Onion Valley we see a larger U-shaped valley underlying a larger V-shaped erosion on top. This formation extends down to about 2200 meters, nearly 600 meters Å 2000 feet below Onion Valley.

Volcanic activity in the Sierras
or More Misconceptions from MindÕs Projections

When I first made my relief map, I stopped just before the huge terminal moraine of Onion Valley. Extending my brainÕs pattern, I assumed that the mountain just went down to a base as mountains do, I thought. I even remembered that happening. Working down with the sixteenth inch foam core, I decided to go to the full extent of the topo map rather than stopping where I had stopped before. My first surprise was the existence of these projections, which I surmise were earlier terminal moraines. I had no idea what they were at the time, but once recreated, I remembered them. Now I knew that we had reached the base and that the mountain would just go down from there. I remembered that too. Whoops! Another surprise.

Below 2200 meters to about 1500 meters when my relief map stopped, I expected to find river based erosional valleys because of all the sediment washed down from above. Plus it is too low to have any ice action. I did find these deeper valleys but I also found something else.

Three million years ago the Sierras began to rise because of separation. In a similar vicinity of time the Pacific Plate pushed the island arcs of the Farallon Plate into the coast of California creating the great heat and pressure necessary for volcanic action. There was volcanic action in Napa; also the pressure created volcanic action in the Sierras.

There have been 5 volcanoes in the High Sierras that have been active in the last 10,000 years, all on the ridge separating the eastern and western Sierras. Upon looking at our relief map, Mount Rixford and the unnamed peak next to it look suspiciously volcanic. For one, although they are on the east west ridge, they both rise to a conic peak, which has been eroded by the glacier to become a horn. Secondly their base is plopped right down on top of this ridge. It seems that our relief map reflects the volcanic action of a few million years ago. Much of the low-lying volcanoes have been completely obliterated. Mount Rixford at 3928 meters Å 13,000 feet apparently was high enough to leave a mark behind.

Seeing these traditional peak-like mountains, which satisfy my instinctual feeling for mountains, next to the huge granite block which is the Sierras, I realize that my conception of mountain was too small to hold my notion of mountain. The upward projection of Mt. Rixford pales before the enormity of the Sierra block.

This leads to my next surprise. Cutting the lower topo forms, below 2200 meters, instead of encountering more of the same, I began experiencing these protrusions, polyps, which would extend a few thousand feet into the valley. I thought I knew the Sierras after these months of cutting and now I find a new landform. The difference between them and what lay above was that the forms were bubbly and rounded compared to the angular protrusions higher up. Additionally these protrusions seemed to issue from one narrow point in the side of the block. (In cutting the forms I got the distinct impression that there had been something liquid leaking out of the granite block. It was as if someone had poked a whole in the chocolate milk carton and the chocolate was oozing out from the point. At first I thought it was an isolated incident but then I experienced the same forms over the whole lower valley.)

My unconfirmed theory is that the same pressure that created volcanoes on the top of the ridge, also pushed through the crust at the base to extrude molten lava. While the evidence of lava flow was obliterated by glacier action higher up, just leaving a few high conic peaks, down at this level below even the destructive power of the Great Glacier, we have the remains of the lava flow covered by sedimentation from above, but leaving its distinctive landforms.

The last of these volcanic polyps finishes out at 1600 meters. We finally reach the sedimentary plane of the valley floor. My logical conception was that once we reached the bottom of the mountain that the sediment that was washed down would cover any variations in the landscape. Silly me, still somehow thinking that I could somehow logically predict Mother Nature. She always surprises me. Here she surprises me with a natural amphitheater, which encloses Boron Springs. Plus there are the subtle gradations of altitude suggestive of lava flow. Once again it is not the simple flat slightly graded plane that I expected. Once again my preconceptions govern my perceptions. Once again Mother Nature comes up with a pleasing surprise. Once again I must let go of my mind grip in order to experience the fullness of Nature. Once again my hand experience has led my brain into a new-found flexibility.

 

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