Glacial Formations -- Geology 101

This page describes kettles, drumlins, moraine, loess, erratics, grooves, and a host of other geological phenomena created by glaciation.

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The information presented on this page is primarily for our hikers in the northern sections of the United States and Canada, to the extent that glaciation shaped the terrain.

Drumlins

Elongated hills of glacial sediment; appear to be elongated oval "humps" if you will. New York State Finger Lakes region has a number of drumlins.

Erratics

Glacial Erratics. Basically, any feature that is located somewhere that it really shouldn't be, as a result of glacial movement. Boulders perched atop a ridge, boulders resting on a tripod of small rocks, balancing rocks...usually these are metamorphic rock that have been dumped somewhere as glaciers moved, melted, or receded.

Kettles

Smooth but noticeably deep pits or potholes formed when a residual chunk of ice was surrounded by fill material. The ice ultimately melted, leaving a pit or pothole in the shape of the ice pocket. Usually round, some might be 50' across, some might be 300'; true glacial kettles will fill with water during spring but dry up during summer. Kettles filled with water year-round are called Kettle Lakes or Kettle Ponds. People who live in areas with lots of Kettle Lakes (Wisconsin, for example) sometimes refer to plain old kettles as "dry kettles."

Loess

Glacial loess is a fine, wind-borne deposit of silt formed along the edge of a glacier. The silt is extremely fine; usually measured in hundredths of a millimeter. The loess occurs where glacial outflows or smaller glaciers occurred. Deposits are homogeneous and show no sign of stratification. Loess "cliffs" can be up to 300' high. Found at random throughout the northern USA. Frequently forms as a deep bluff of fine gray "powder."

Moraine

Piles of gravel and/or rock left behind by retreating glaciers. Morain Lakes were formed when a moraine naturally blocks a stream or river; a moraine might fill part of a valley, forming a natural dam and creating a lake.

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