Glacial Cirque of Grinnell Glacier, Glacier National Park, Montana.

This spot has got to be one of my favorite places anywhere. It's alpine, it's glacial, it's icy, and the bedrock... it's just incredible!

This photo shows the outlet of the tarn beneath Grinnell Glacier --one of those glaciers that is both accessible and photogenic, so its retreat has been documented by a zillion photographers. The surrounding bedrock is dolomite of the Helena Formation, one of the Proterozoic units of the Belt Supergroup. Not shown in this photo, but less than a minute's walk away are some gorgeous stromatalites, fossilized mats of algae, some of Earth's earliest lifeforms. Click here to read more about the Belt Supergroup and stromatalites in Glacier National Park. Or, if you just want to see stromatalites, go to my geology photo search page and type in "stromatalite"!

There's also that prominent stripe halfway up the cliff. It's a sill of diorite, called the Purcell Sill, that intruded these rocks about 1.1 billion years ago. Notice the white zone in the dolomite on either side of the sill; it's a bleached zone from the heat of the intrusion.


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