Brookes Bay and Glacier
Brooks Bay, on the 16th of November, offered us something which we hadn't seen in a few days - sunshine! For the most part, our trip around Tierra del Fuego was done under cloudy conditions, with some rain but not too much. Some of my best pictures of glaciers and glacial features were taken in Brookes Bay, including the North Brooks Glacier.
Like Pia Fjord and Garibaldi Fjord, Brooks Bay also offered us ample opportunity to view glaciers up close and see plenty of waterfalls, while also presenting some features we hadn't seen before. We once again landed on shore, this time for a close look at the North Brooks Glacier.
A U-shaped valley describes the shape of the valley that forms from erosion by glaciers. There were many examples throughout the Tierra del Fuego region.
Ice fall deposits were also seen. Many of these form as the Darwin Ice Sheet advances and calves off above a steep slope or cliff. The falling ice collects in a pile down below. If enough of the falling ice collects at the base of the slope, the ice will once again begin to flow as a glacier. This is known as a reconstituted glacier, and Brooks Bay has an excellent example of one.
Moraines are erosional debris (sand, gravel and rock) that are carried along by the glacier. They form along the sides and bottom of the glacier as the ice flows down the valley. The moraines along either side of the glacier are termed lateral moraines. The North Brooks Glacier lateral moraine was interesting in that it was made up of at least three, possibly four, lateral moraines. If you look closely, you will see a line of rocky material in the center of the picture with vegetation just off to the left - that's one moraine. The second line of rocky material is off on the left side of the picture - that's two. The area immediately above the second moraine has low vegetation on it, but no trees - that's three. The area that might contain moraine number four is in the vegetation area between moraines one and two. There is a faint line of rocky material in this that might be another moraine. The multiple moraines tell us that the North Brooks Glacier has advanced and retreated at least three time in the recent past. Each time the glacier advanced, it deposited a new lateral moraine on top of the older moraines.
Another feature that was seen here and not elsewhere was a kame. Kames are deposits of silt and sediment that form in a variety of ways. The kame at the North Brooks Glacier appears to have formed as material washed off of the surface of the glacier during melting in the summer. During the summer the glacier retreats due to this melting. Our guides reported that in the later summer months it is possible to walk completely around this kame. In the winter the glacier advances enough to abut against the kame or over-run it. The line of sediment in the water at the bottom of the picture is an end moraine, and indicates that the glacier has advanced to this point in the recent past before retreating to its present position.