Tuesday, August 30, 2011

A boat trip to the fjord

Most of the rapid changes in glaciers that we are currently observing are related to changes in the oceans. So it is increasingly necessary to make direct observations of ocean conditions in front of glaciers. But that's not always so easy:

The answer is to hire a small boat that can handle impact from ice
and a capable crew (skipper Hans and deck hand Peter):

We spent a week in the inner fjord measuring temperatures, salinities and currents in the ocean.
We also deployed some drifters that will float out with the water. They report their positions with measurements of the upper water column every half hour via Iridium satellites.
We spent the nights at a protected little bay, with beautiful sunsets (before the weather turned lousy), and reindeer and fishing nearby. Peter, the Greenlandic deck hand, is also an avid hunter and fisherman and provided us with fresh food.

Near our anchorage, one could still find the remains of foundations from Norse settlements. The Norse had lived in this area for several hundred years during the medieval optimum, and finally disappeared with only few traces left.

Monday, August 29, 2011

How fast does a glacier flow?

One of the main things we are often interested in is the speed of glaciers, and how variable it is. For that we use a variety of methods. GPS works really well, but low down on tidewater glaciers, there are so many crevasses that we don't like to leave expensive instruments. This year we had an exciting opportunity to test a new method. It measures the displacement of ice by looking at the difference in returned radar phase. It is possible to get a velocity field within a few minutes of measurements only. The image below shows the instrument, which we had on loan from Gamma Remote Sensing.

To verify the results of the radar we also did some more traditional surveying. For this we deployed targets onto ice towers (seracs) from a hovering helicopter. These targets consist of a prism reflector, which is then surveyed with a total station from the side of the glacier.

Sunday, August 28, 2011

Back in Nuuk

We're back in Nuuk, Greenland. This is the key field work for our proposal, in which we try to better understand ice-ocean interaction. The planned work involves detailed observations of conditions in the fjord and of the variation and details of glacier flow near its front. We have two teams, one camped at the glacier front and one in a small boat.
Getting out was delayed a bit. Nuuk has been having problems with low fog. Even when we finally left, it was through a small hole in the fog. Just a little distance away from town, the weather turned nice.

The first task was to fly back to GPS stations that are far up on the ice and that are designed to run all year. At this particular station, a little over 1.5 m of ice had melted. The box with batteries and instruments slid around a bit, but everything was working fine. We don't always find things in such nice condition!The main work is to observe conditions at the glacier front, however. One important observation is the release of fresh water from the base of the glacier. Because it is fresh, it raises right to the top and creates a surface plume at the glacier front. The upwelling water brings lots of stuff with it, and when we fly over, we can sometimes see hundreds of birds feeding there.

Tuesday, August 16, 2011

Susitna Glacier

Ok, so this comes a bit late, but in June I joined Sam Herreid on a quick trip to Susitna Glacier in the Alaska Range. We were putting in a camera to observe the glacier. It's a surge-type glacier, which means that it can accelerate to almost 100 times its normal rate of flow in a few months. It last did that in the 1940s. The combination of normal flow and surges creates these beautiful looped moraines.Susitna Glacier is also interesting, because there are serious efforts under way to build Alaska's largest hydroelectric power plant in its drainage area. This requires some careful thought about how the discharge will evolve, as the glaciers in this area are generally retreating, and how much sediment is being put into the river, in particular if another surge should occur.
We put in the camera by piggy-backing on another project, which got us a helicopter ride in. On the way back we relied on a pack raft, a first one for me.