Reading the Rocks

yosemite-history-of-glaciers

The view from Olmsted Point includes a slew of glacial erratics. Photo by Grant Ordelheide

 

Signs of Yosemite’s glacial past are everywhere. Follow these tips on what to look for and where to find them. 

Glacial erratics

Boulders that were once carried by glaciers, then haphazardly deposited across the landscape

Where: Olmsted Point

Chatter marks

Gouges left on irregular granite surfaces by moving ice or large boulders; usually on the down-canyon side of a dome or slope

Where: Lembert Dome 

Glacial polish

Patches of shiny surfaces on granite that were wiped clean by moving glaciers; often located on the up-canyon side of a dome or rocky slope

Where: Pothole Dome near Tuolumne Meadows or along Tioga Road across from Olmsted Point

Subglacial water polish

Glacial polish that appears fluted or sculpted and was formed by water flowing long ago beneath the ice sheet of a glacier

Where: Pothole Dome

Exfoliation

Eroded landscape characterized by descending layers of rounded cracks; picture a peeled onion

Where: Along Tioga Road west of Tenaya Lake 

Yosemite Cathedral Lake and Cathedral Peak with Glacial Nunataks

Yosemite Cathedral Lake and Cathedral Peak with Glacial Nunataks. Photo by Steve Dunleavy (Flickr: Cathedral Peak, Yosemite National Park) [CC-BY-2.0], via Wikimedia Commons

Nunataks

Mountain peaks that were high enough to escape advancing glaciers, which left their jagged, sawtooth peaks intact

Where: Cathedral Peak and the Clark Range

Kettles

Small lakes in scooped-out depressions that were left by melting glaciers

Where: Gaylor Lakes and Dana Meadows

Pothole on Pothole Dome

Subglacial pothole on Pothole Dome. Photo Public Domain

Potholes

Dry, bowl-shaped depressions that were carved into granite slopes when the rock was gouged by  stones swirling around in melting glaciers

Where: Pothole Dome (of course)

Hanging valley

A tributary of a main river channel or valley that was down-cut faster by glacial activity than the main channel, leaving the tributary glacier higher and “hanging.”

Where: Bridalveil Fall

Rouche moutonnée

An asymmetrical ridge that was smoothed by glaciers. These granite formations are often mistaken as domes.

Where: Lembert Dome

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