The Glacial Features of
Martha’s Vineyard - Part Three
A topographic map of MV clearly shows the bottoms in the outwash
plain, as well as the moraines. Can you see where the actual edge of
the ice would have been?
The outwash plains of the Vineyard today are characterized by the flat,
sandy central (interior) and southern part of the island.
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The outwash plain
is an ideal place to
build an airport.
The moraine of the Vineyard today is characterized by the hilly areas,
especially up-island (Chilmark, West Tisbury).
The moraine is an ideal place for sledding in the winter!
Notice all the boulders in the moraine. They are called erratics. Most
of them are from far away. How did they get here?
Many of these erratics have been put to good use by people.
Some erratics are enormous. What is strong enough to move such
massive rocks such great distances?
Another key feature of the moraine is called a “kettle hole”. You know
them better as the freshwater ponds of the Vineyard.
How could such a hole form? Why are they only found in the moraine
(not in the outwash)?
Not all kettle holes contain water.
This diagram shows how a kettle hole can form.
Summary: Moraine vs. Outwash
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Deposited directly by the
ice.
Made of sand, silt,
gravel, rocks and
boulders (erratics) of all
sizes.
Hilly landscape.
Northeastern and
northwestern sides of
MV.
Contain kettle holes
(freshwater ponds).
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Deposited by glacial
meltwater.
Form in front of the ice.
Mostly sand and silt.
Flat landscape.
Central and southern
parts of MV
Contain bottoms (dried
up streams of glacial
meltwater).