We join the Corps crew on the M/V Strong in the morning. We head south on the Mississippi
River to south of Crowley’s Ridge, a remnant of the erosional episodic path taken
by the Mississippi River during its developmental history. However, Crowley’s Ridge
is suspected of being fault-driven. When two faults cause the land between it to
rise, it is called a horst. This is unlike the faults controlling the Reelfoot Rift, which dropped, called
a graben. Crowley’s Ridge is believed to be a horst. We wanted to get south of the ridge
so that when we headed upstream, hopefully we would capture the possible faults controlling
the formation of Crowley’s Ridge and the numerous other faults already mapped in that
The seismic array, Huck and Jim, worked like a charm. Energy was being sent through
the river and into the subsurface every 10 seconds. The hydrophones recorded the
energy signal that bounced back from the deep geologic layers. Results are final
when the hydrophones record the returning energy. The data must be filtered and processed.
This takes a long time and will be done over a number of months after the river trip.
However, we are not completely blind to what is returning. In what we do see, we
see structure. And if you see something in as we do in the data before it is processed,
you have a really good chance of seeing some great things once processed.
The Chirp was not working. We carefully took the signal box apart to poke at the
electrical insides. Still no go. After placing volt meter probes here and there,
we determined that the Chirp emitter was shorted. Unlike the signal box, the Chirp
emitter is NOT something you take apart. A replacement Chirp was ordered from Canada,
to arrive in 2-3 days.
Due to complications and our first time in production mode, we never quite made it
up to Helena. For one thing, we have to go really, really slowly. In the water,
we need to stay around 2 mph upstream (headway). Due to the current, we could not
accomplish this, as Huck would dive wildly under water and fish back and forth. This
movement through the water created noise on the hydrophones. Just like a TV with
snow, noise on our seismic data would make it difficult to see things.
We tried something. Odd…but why not try it. Facing upstream, we went backwards down
the river. Can’t turn the boat around because we would not have the control needed
to better steer the boat at such low velocities. So, we tested our theory of going
in reverse down the Mississippi River. It worked. Huck stayed up, Jim seemed happy,
and we obtained the velocity we needed. The data capture was absolutely beautiful.
Better than if we were going forward. The Corps was just driving in reverse. Man
Plans were revamped. What was needed logistically to go backwards?