PURGATORY CHASM
by Caitie Sams and Ali Quirk
Glacial Features
DEPOSITIONAL FEATURES:
Till- This is material dragged along the bottom of glaciers. It is poorly sorted and often contains sand, clay, and pebbles. This can be seen more towards the end of the trail and takes the form of pebbles and small rocks.
Erratics- these are boulders that fall on the glacier and eventually slide off and get dropped behind as the glacier melts. They are often large boulders that look nothing like their surroundings. The erratic we found is made of alaskite (to learn more click here), which does not match the boulders found on the walls of the chasm.
EROSIONAL FEATURES:
Striations- These features are scratches on the surface of rocks. They form when sediment that is frozen to the bottom of glaciers is dragged across the bedrock present and the walls along the sides. These striations were found on the wall of the chasm as well as along the bottom.
This erratic made of alaskite doesn't match the walls of the chasm, like the other boulders in the area. So it must have been transported to the area from glacial movement.
This poorly sorted material found in the chasm is till indicating that glaciers moved over the area leaving this behind.
