Glacial Sluiceway – A valley or channel that conducted large
amounts of glacial meltwater that may or may not be occupied by a
modern stream; commonly associated with one or more ice
margins.
Lacustrine Plain – A plain of alluvial sediments
originally formed in a lacustrine environment, that is, as the bed
of a lake, but from which the water has disappeared.
Glacial sluiceways carried huge quantities of outwash (soil, sands,
silts, gravels, etc.) from glaciers. This outwash was eventually
deposited along the channel as alluvium. The powerful forces of
glaciers and their meltwater are visible today across Indiana as
till planes, alluvial floodplains, terraces and other land
forms.
Occasionally the outlet of a glacial sluiceway or tributary would
become clogged with ice or sediment and a glacial lake would form.
In these lacustrine environments the outwash sediments would settle
to the bottom of the lake.
Once the waters disappeared from the lake and the soils dried,
strong glacial winds would blow the lighter materials away
eventually depositing them as shallow layers of loess (fine, rich,
limey soils) across the landscape.
Geological studies have determined that several glacial lakes were
present in Indiana during the two most recent glacial events, the
Wisconsin Stage and the Illinoian Stage. During the most recent of
these glacial stages, the Wisconsin (between approximately 50,000
to 10,000 years ago), glacial lakes tended to occur mainly in the
valley tributaries of the large channels as a result of valley
trains (built up outwash sediments) which would sometimes block the
tributary outlets.
During the earlier Illinoian Stage (between approx. 300,000 to
140,000 years ago), smaller river valleys, for example, Salt Creek,
Blue River, and Patoka River played a larger role as glacial
sluiceways along with larger ones such as the White, Wabash and
Ohio. The smaller channels carried more outwash during the
Illinoian glacial Stage primarily because the ice sheet advanced
much farther southwest and southeast during this period.
The glacial lakes which formed during the Illinois Stage most often
occurred in the main channel rather than the tributary valleys.
These glacial impoundments were usually the result of blockages of
the main channel outlet by the southwestern lobe of the Illinoian
Glacier.
A glacial lake developed in the Patoka valley during the peak of
Illinoian Glaciation. Called Glacial Lake Patoka, the lake began in
Pike County where its sluiceway outlet was blocked by the advancing
lobe of the glacier (approximately N 38° 22.816', W 087° 13.032').
It ended in eastern Dubois County somewhere near the Dam of present
day Patoka Lake.
To log this Earthcache as a FIND you must correctly accomplish
BOTH the following task:
#1) Determine the straight-line length (rounded to the nearest
mile) of Glacial Lake Patoka. Send me an email with your answer.
DO NOT post the answer in your cache log.
#2) Post a photo (optional) with Patoka Lake visible in the
background.
Credit for a FIND is not official until requirement #1 is correctly
fulfilled.