ISLANDS IN THE
STREAM
This is no mere cache, it is an EarthCache:
an educational form of a virtual cache. The reward for these caches
is learning more about the planet on which we live - its
landscapes, its geology or the minerals and fossils that are found
there. They are developed in association with the Geological
Society of America.
This Geocache will
will take you to a Fluvial Island in the Wabash River in Indiana.
There are many more or less permanent islands in the Wabash in this
region and some are named, such as Potter Island near Wabash, Rock
Island near Peru and Biddle Island near Logansport. Some even
support buildings.
What is
a Fluvial Island?
A Fluvial Island is a Geomorphic feature elevated from and
surrounded by stream-channel branches that persists sufficiently
long to permit the establishment of permanent vegetation
Our island has large trees growing on it. It is partially
flooded every year due to snow melt, spring thaws and the operation
of the Huntington Dam upstream.
At it's leeward end you can observe a new channel and the
beginning of a new island.
These types of Islands can be formed by a number of methods
or combinations of methods:
1) Avulsion occurs by incision and channel straightening
during erosive flood, initiated by flow diversion by debris
dams.
2) Gradual degradation of channel branches-- Steady
evacuation of deposits in channels that bound a higher
within-channel surface.
3) Lateral shifts in channel position e.g. channel migration
and meander cut-off during normal discharge isolate a central
surface higher than the channel branches surrounding it.
4) Stabilization of a riffle, sand or gravel bars by
accretion and vegetation establishment during a period of
non-erosive peak discharges.
5) Steady degradation of channel branches along preferred
paths of bedrock fractures -- Typical for non-alluvial
channels.
6) Rapid incision of channel branches into deposited
sediments during recession of a flood -- Most common in small
streams.
7) Lee deposition at channel obstruction -- Most common in
widened, braided channels.
8) Deposition of various features by mass movement e.g.
rockfall -- restricted to lowlands, rare.
In order to log this cache:
1. Upload a photo of yourself, showing
your face, with your GPSr, and the Island in the Background.
2. Send the owner an email with your estimate of the length and
width of the island at the time of your visit.
3. Include in your email the number(s) of the method of island
development you think is in process here, and why.
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