Geohazards in Bangladesh

Everyone pitches in to deploy the 50-m long streamer by hand.

We have been sailing along collecting data, but so far the data quality is poor due to shallow gas in the sediments.  We thought we might have some problems with gas, but the problem is more widespread than we expected.  We are now out of the inland summer lake where we met the boat and will soon try profiles up the Indian border where we expect a buried fault.  We may pick up a local pilot that knows which ones are navigable. We hope the environment is different enough that we can get good data. A Meanwhile we have been changing the sound source to try to get better data.  Depending how it goes, we will continue around here or head to a different part of the country.  In contrast, the ship and company is great.  Working primarily daylight hours with systems are running flawlessly, we do not have formal watches.  It is only for deploying the seismic data and retrieving it that all hands are needed.  A small group takes care of maintaining the running equipment.  Voldhard Spiess keeps trying different processing to improve the data.  We start up at 6:00 AM and continue until around sunset or reaching our target stopping town. During the day, we are continuously having discussions on the science, with each of us bringing different expertise.  The data, methods to improve it and where to go are ongoing subjects of discussions.  With Steve and Humayun here, we can also plan for future parts of the project.

The top shows a ferry docking at Jamalganj as we sailed by at high water. The water is almost at street level. The bottom shows the ferry crossing as it looked in February, when we had to scramble down the embankment to the river.

Last night, we stopped in Jamalganj, where I helped install one of our compaction meters in February. Back then, the river was probably 15 feet lower.  A large group came ashore with Humayun and myself to see the site.  It is my third time in this now familiar town. Waiting for Aziz, the caretaker, we attracted a large crowd.  Walking to the site as darkness fell (and pretty quickly in the tropics), we discovered Aziz had brought a crescent wrench rather than a pipe wrench.  With typical Bangladeshi ingenuity, glancing blows with a hammer loosened the cap on the pipe and we were able to retrieve the piezometers and their water level data.  We then visited the former jail cell with its massive iron bars where the GPS receiver is and Humayun downloaded that data.  Shaheen, Aziz’s son was away in Dhaka, but we retrieved the laptop with the compaction data and copied it, too.  The biggest change in the site is that instead of mud everywhere, the site was now covered in green.  A small bright spot of success in the trip.

Humayun in the small room off the main jail cell downloading the GPS data from the compaction site to his laptop.

Rabi on our "launch" watching the approaching the M/V Kokilmoni

After a great field season last winter, we had an extraordinary opportunity this fall, a research cruise on the Bangladeshi rivers collecting geophysical data. We are using the same technique that Lamont uses on its ship, the R/V Marcus Langseth, but a mini version.  The basic idea is to use sound waves from bursts of compressed air to bounce off the layers of sediment below the surface and to record it on a string of microphones towed behind the ship called a streamer.  The difference is scale.  While the Langseth can tow four 6-km long streamers, we have one 50-m streamer.  Our source is similarly reduced.  The system we are using, built by Bremen University in Germany, will only see a few hundred meters below the surface, but with great detail.  The cruise is taking place on the M/V Kokilmoni, an 85-ft long boat built for tourist cruises of the Sundarban mangrove forest, home of the Bengal tiger.

While the Bremen group and a few of the Americans will stay on the entire 25-day cruise, the rest of us have the opportunity to join and leave the ship during the cruise, something not possible in the middle of the ocean.  Due to other commitments and, in part, not wanting to be there for the inevitable problems at the beginning of the cruise like this, joined the ship today, over a week after the scheduled start (less than as week after the actual start).  Nano Seeber, Rafael Almeida and myself left Lamont on Monday, Sept 12 and after a long set of flights arrived in Dhaka at 4:00 AM Wednesday morning.  We dropped some equipment off at Dhaka University, picked up Humayun Akhter and a student and headed off to find the ship.  This was not as easy as we thought.  They were entering the area of the Sylhet Basin that floods every year and there were not too many places where car and boat.  Talking while driving north, we came up with three places where we could meet.  They past the first one hours before we could get the, but worked out a plan for number two, saving probably 5 more hours of driving to get to the third.  We drove out to the meeting place on ever-smaller roads finally ending at a port on this vast inland lake.  Using cell phone towers, the tall chimneys of brick factories that are now islands and a hospital ship, we finally located each other and they sent their small boat to pick up us.  It brought Dhiman  and Pritam as well, returning to Dhaka University with Babu, our driver.

View of our landmarks, the brick factory chimneys and telephone poles along the flooded Dhanu River

Welcomed on board, we got underway following the markings of where the river channel is across the broad expanse of water.  Patches of grass, the occasional tree, islands of homes and lines of telephone poles dot the area that will become fertile farmland again in a few months.  I’ve known of the flooding worked on calculations about it, and heard stories, but this was the first time I saw it for myself.  I’ve always been here in the cool, dry winter-early spring.  It is truly amazing and filled with an amphibious population traveling by bus and rickshaw in winter and boat in summer.

Steve Goodbred and Volkhard Spiess view our data in the lab/mess.