Today was interesting. Near Hickman, KY, the Mississippi River rolls over an outcrop
of clay(?) and plunges beneath its muddy surface 150 ft., scouring into the subsurface.
The Mississippi River does not form a waterfall, but if you watch the bubbles floating
on the water’s surface, you will see them going upstream at times. Whirlpools were
everywhere. This plunge pool creates problems for barge traffic as you can imagine.
We were to make three passes across the plunge pool to understand its origin and what,
if anything, could be done to improve navigation. Eddies and whirlpools proved difficult
in controlling the boat and the seismic equipment. Additionally, the flooding in
the north was causing the river to rise. Debris (trees) will park themselves on the
banks of the Mississippi River during a falling stage. Yet when the river rises,
the debris is picked back up and carried downstream. This bank debris and that floating
down from the flooded areas kept the Echo (chaser boat) dancing across the muddy waters,
hooking trees (literally whole trees!) away from the seismic equipment.
It will take processing the data to determine what structure exists at the plunge
pool. The Chirp proved very useful, recording layering in the shallow subsurface.
It is too early to draw any conclusive findings.