Friday Rock Blogging: Glacial Polish
Glaciers look regal and calm, or at least, that’s the canonical photograph: blue-tinted light refracted around a majestic pile of ice. And they basically are, but like most regal majesties, glaciers are also cruel oppressors who grind the peasantry under their boots. And by “peasantry” I mean “rocks” and by “boots” I mean “rocks and ice”.
When glaciers retreat, they leave behind a variety of characteristic marks, all of which have funny names: drumlins and eskers and cwms on a large scale, chatter marks and striations and polish* on a smaller scale. There’s nothing special about the process that produces glacial polish; it’s simply dust and grit on the bottom of the glacier acting as a piece of sandpaper as the glacier goes wherever it’s going.
The images here are both from Yosemite, and the second one is supposed to be a particularly accessible outcrop, worth visiting if you’re up there for pedagogical purposes.
*Okay, “polish” isn’t funny.