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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.


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.


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.


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."


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."


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.

Roadside Geology -- If you travel at all, you absolutely have to start building your library of Roadside Geology Books. These are the fascinating geological wonders that professional geologists know about, but us amateurs drive right past without a clue. At the very least you ought to get the guide for your home state. If you are a rock collector, or just an armchair geologist, these books are more important than your GPS. The link goes to Amazon, so you can click safely. Your purchase earns a few cents toward operating this website, at no added cost to you.

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