The last time we visited the southern part of the East Africa Rift, we were responding to an unusual series of earthquakes in December 2009 that shook northern Malawi. The faults responsible for these events had not produced any earthquakes historically, and thus caught everyone by surprise. The unexpected occurrence of earthquakes on these faults highlights our poor overall understanding of how the African continent is slowly stretching and breaking apart.
This time, we return to this part of the rift system as a part of a more comprehensive effort to understand the underpinnings of this continental rift using a spectrum of geological and geophysical tools and involving a big international team of scientists from the U.S., Tanzania and Malawi. In the coming three weeks, we plan to deploy ~15 seismometers in southwest Tanzania around the Rungwe volcanic province, the southernmost volcanism in the East Africa Rift system. These stations will record small local earthquakes associated with active shifting of faults and moving of magmas at depth. They will also record distant earthquakes that can be used to create images of structures beneath Earth’s surface and map the faults and magmas.
144 miles separates Kangerlussuaq from Raven Camp. Not far really, just 144 miles – like traveling from the southern tip of New York City up to Albany. Flying at 270 knots we can be there in about half an hour, no time at all, and yet to the casual observer they seem worlds apart.
Kanger sits nestled in the arm of Sondrestrom Fjord, where over the years Russell Glacier has found the soft belly in the rock base, wearing the surface down flat and pushing the rock flour out to sea. Currently the tip of Russell Glacier is a full 20 kms (14 mi) up the fjord. In the summer months, as research teams move through the village, glacial meltwater fills the carved channel that borders the small town.
Meltwater Rushing Behind Kangerlussuaq, Greenland
“Summer meltwater from Russell Glacier rushes around the edge of Kangerlussuaq.”
Although modest in size by our standards, Kangerlussuaq is a transportation hub for Greenland, and has a steady year-round population of ~500 residents.
Raven Camp sits high up on the Greenland Ice Sheet on a frozen bed of ice, almost 2 kms thick (~1 mi) and millions of years in the making. At almost 7,000 feet of elevation, no seasonal change will bring a rushing river or a population to match that of Kangerlussuaq, but summer research does bring an influx of summer scientists, swelling the population beyond the posted total of 2. With a handful of tents and collapsible housing structures, Raven Camp is a “summer town.”
Today we fly to Raven Camp to complete a survey grid over the ice landing strip. A year ago the camp staff detected several cracks (crevasses) in the ice running perpendicular to the airstrip. Crevasses are to be expected around the edges of an ice sheet, where the ice is faster flowing, however, at this elevation and this far inland it is more unusual. Published data for ice movement in this area shows at the base the ice is moving about 2.5 cm a day, while at the surface ice is moving closer to 7 cm a day. It is no surprise that the ice at the base moves more slowly, a result of the increased friction at the bed causing the ice to stick and slow.
Currently measuring only 10 cms across, it certainly doesn’t seem that this could cause much trouble. But if the crevasses are deep and continue to widen, they will threaten the landing strip. A team of scientists has been collecting measurements on the ground to see if these rates are changing (2013 polarfield blog1); our job is to survey the area with our instruments. The Shallow Ice Radar and the infrared camera collect the depth of the cracks and the temperature differences as the cracks move deeper into the ice. Pulling all this data together will help us understand what is happening to the ice in this area.
Our flight grid will be flown low, at 1,000 ft. above the ice surface, one third our normal survey elevation. Two East/West lines are flown perpendicular to the landing strip at 600 meters apart. Then three tie lines are flown parallel to the runway at 100 meters apart.
Once the grid is complete, we land on the airstrip, testing the seal on the pod door and collecting some camp cargo. The landing is smooth.
Temperatures today at Raven are a warm 1°C. The snow has lost some of the crispness we had experienced when we had landed in April to install a GPS on the ice. The pod is inspected. The camp looks all but abandoned, yet a snow vehicle appears with cargo that is stashed and secured for transit. While the cargo is loaded, we snap a quick IcePod team photo.
The new eight-bladed propellers on Skier 92 do their job and the take-off is smooth for our return to Kangerlussuaq, just 144 miles, 30 minutes of transit, and yet seemingly worlds apart.
1 For more on the science being collected on the ground on ice movement: http://www.polarfield.com/blog/tag/greenland-ice-cap/
For more on IcePod: http://www.ldeo.columbia.edu
The Langseth Galicia 3D seismic cruise is winding down. By tomorrow we will be back at the dock in Vigo. Like most seagoing science, we will miss the ship experience, we will miss the new colleagues we have met, we will look forward to getting back on shore, and for many of us the awesome multi-year task of processing, interpreting, and publishing the boatload of data we have acquired.
This is an example of the data we have collected. Right is to the East and left is to the West. This is a cross section of the Earth about 65 km long. The blue is water. The water depth here is about 5 km. The red and gray colors are a cross section of the rocks below the water. The flat layers are sedimentary rocks. The lumpy bumps (that is a technical term!) consist of blocks of continental crust and of the mantle.
We thank the Langseth’s Captain and crew for making this possible! These are men and women who live on the sea, and who share their ocean world with us for a month or two. Every now and then, when you can walk 100 meters in a straight line, ask yourself, “Where is the Langseth now, and who is steering the ship, or keeping the engines running, or keeping the deck ship-shape, or providing good food, or every other important task on the ship?” Under your breath say thank you for the experience you had on Langseth.
We thank Robert and his technical team. They worked tirelessly to assemble the 24 km of hydrophone streamer that hears the reflections from the Earth, the 40 or so airguns that make the booms, and all the rigging it takes to tow them spread out behind the ship over 600 meters wide and 7000 meters long. That was just the start. Then they operated the electronic equipment that received the seismic data and recorded it for the scientists. Without them we could not do the science we love.
Thank you to the Science Party. We had a total of 20 scientists, including undergraduate students, graduate students, post-docs, researchers, and professors. On Leg 1 we had 14 scientists and on Leg 2 we had 10 scientists. Four scientists weathered both legs. Six joined us for Leg 2. I am very grateful for all your efforts on behalf of the Galicia 3D science. I hope that you learned a lot, had a good time, and met other scientists for the first time. I suspect that we will meet one another many times in the future.I look forward to that!
This is the Technical team and the Science team for Langseth Leg 2.
I want to thank the Protected Species Observers for sailing with us. They spent countless hours in the observing tower, high above any other part of the ship. They have sighted hundreds of whales, but most did not come close to the ship. It is windy and cold up there, but their role is important for making sure that collecting our scientific data does not interfere with the creatures who call the ocean home.
Thank you for sending your loved ones off on the Langseth. I can certify that they now know how to do their own laundry and to clean up their cabin before they leave the ship. During the weekly emergency drill, they run quickly up to the muster station on deck and put on safety gear. I recommend that you continue to enforce these behaviors ruthlessly! They will forget them if you let them slack-off. On the other hand, they did not have to cook their own food, or wash and dry their dishes. You will still have to work on these behaviors!
As I write this from the Langseth, we should remember that the Galicia 3D experiment goes on. Our colleagues from GEOMAR and University of Southampton will be on the FS Poseidon from 25 August to 10 September. They will be recovering the 78 Ocean Bottom Seismometers that are still on the bottom (on purpose!). They have been recording approximately 150,000 airgun array shots fired by the Langseth. I know what you are thinking. “How many total recordings of shots are recorded in all the OBS’s?” That would be about 11.7 million shot recordings. This will keep the OBS scientists busy for a while!
I particularly want to thank James Gibson for creating this blog. It has reached out to our friends and to strangers. We plan to keep the blog alive. This project will continue for years.
Best regards,Dale SawyerRice University