Fourth Report -- May 10, 2004

The track of the echo sounder shows the submarine volcano rising from 1000m water depth to a peak with water depth of 250m only. photo: Gemma Kirkwood

Dr. Gerd Krahmann, of the Lamont-Doherty Earth Observatory
aboard the R/V L.M. Gould, Weddell Sea, Antarctica...

Afternoon May 10, 2004
Punta Arenas

It has been a few days since I wrote my last report. A number of things have happened since: the geologists on board were able to continue their work in the region northeast of the Antarctic Peninsula; we visited an undersea mountain that the group had first discovered four years ago. On this visit, we were able to confirm that it is a submarine volcano showing signs of recent activity. Unfortunately, the weather deteriorated over these days, forcing us to leave the work area a day early. We navigated Drake Passage on our way home to Punta Arenas (Chile) in a crossing described by the crew as one of the worst.

50mph winds made the approach of the pilot for Magellan Strait tricky and dangerous as he had to jump from ship to ship with no support at all. photo: Gerd Krahmann

The geological work northeast of the Antarctic Peninsula continued for several days as I have described in the third report from the field. The scientists and six students worked in day and night shifts to complete a survey of the area. They used the echo sounder of the ship, ordinarily used for navigation, as a scientific tool. The sound waves sent out from a transducer in the ship's hull are reflected by the sea floor. The time it takes for the sound to travel from the ship to the sea floor and back indicates the water depth. Geologists don't use the time measurement but rather the way in which the sound is reflected. A hard rocky sea floor reflects the sound in a single sharp echo, while a muddy bottom results in a more diffuse echo. In locations with muddy reflections, the Smith/Macintyre grabs (see picture in third report) were used to take samples of the mud.

After the survey was finished we steamed southward to an area where the group had mapped the water depths four years prior. During that survey, they had encountered a particular feature. In a wide and deep submarine channel, a seamount rose several hundred meters from the sea floor. As the channel had likely been carved out by large glaciers during the last ice age, this seamount must be very young in geological terms. The only way it could have been created was by an underwater volcano. But to prove this, a rock sample from the seamount was necessary.

ARSV Laurence M. Gould (front) and RVIB Nathaniel B. Palmer (back) are the two ships run by the Edison Chouest Offshore shipping company and chartered by the National Science Foundation to provide highly capable and flexible research platforms in the Southern Ocean. LDEO scientists are frequent guests on both of them. photo: Gerd Krahmann

In deteriorating weather, we were able to lower and tow a video camera over the sea mount producing unique footage on the fauna and flora. Subsequently, a dredge was lowered and pulled across the rocky floor. The collected rocks clearly showed the volcanic origin of the seamount. Some of them even indicated that they had been formed within the past 100 years. I had another hint that the volcano might still be active. A probe attached to the camera sled measured areas of slightly elevated temperatures on both sides of the volcano. Footage from the camera has been sent to the National Science Foundation and is being published jointly by the participating institutions.

Sadly, the increasing winds forced us to stop all scientific work. As the weather forecast indicated no change to the better for the next few days, the chief scientist decided to leave the work area and head north to Punta Arenas. During the crossing of Drake Passage, we were hit by winds regularly blowing at speeds of more than 60mph causing the waves to reach heights of 30 feet. As wind and waves always came from the side, the ship was rolling heavily -- sometimes reaching angles upward of 30 degrees. Seasickness hit most of us and all were happy to reach the shelter of the southern tip of South America after 3 stormy days and nights. Yesterday we finally arrived in Punta Arenas and docked next to the big sister (RVIB Nathaniel B. Palmer) of our ship (ARSV Laurence M. Gould).

Gerd Krahmann, LDEO Group Leader