Mt. Discovery vs. Mt. Rainier

We have a beautiful view out the window in our lab. The sun never rises very high on the horizon, so for much of the day everything has a nice pink or orange hue. Looking to the south we can see the McMurdo Ice Shelf in the distance. Directly across from us are Mt. Discovery and Brown Peninsula, and north of them is the majestic looking Royal Society Range. Behind Mt. Discovery and the RS Range are the McMurdo Dry Valleys, a bizarre polar desert that we plan to visit in 5 or 6 weeks. One thing that strikes us every single day is how similar Mt. Discovery looks to Mt. Rainier, an emblematic mountain outside of Seattle.

Mt. Rainier, in the state of Washington.

Although not as famous as its neighbor Mt. Saint Helens, which erupted catastrophically in 1980, Mt. Rainier is an active volcano. Its distinctive shape is typical of stratovolcanoes, a special type of volcano characterized by highly viscous lavas (and very explosive eruptions). This high viscosity does not allow the lava to flow in the manner of the volcanoes of the South Pacific, termed shield volcanoes. As a result the sides of the volcano build up over time and can become quite steep. So is Mt. Discovery also a stratovolcano?

I don’t know a whole lot about volcanoes so I did a little looking around today while Shelly kept things moving along in the lab. As with many geological features in Antarctica I could only find a little public information online. A short blurb on the Oregon State University website notes that Mt. Discovery, like the more famous and active nearby volcano Mt. Erebus, is on a rift system that splits the continent. This explains why there are volcanoes near McMurdo, but doesn’t tell us much about type. Along a rift in Iceland stratovolcanoes and shield volcanoes exist side by side. I did find an article by a Japanese geologist in 1972 indicating that the McMurdo area volcanoes are typically composed of olivine-basalts and the minerals trachyte, kenyte, and phonolite. Olivine-basalt sounds suspiciously like a shield volcano. I wasn’t familiar with the other minerals but when I looked them up I found that they are silicate rich (as opposed to iron rich, like olivine), a clear mark of a stratovolcano. It’s the silicate nature of stratovolcano lava that results in high viscosity and explosive eruptions.

After a bit more searching I finally found what I needed, a 1975 article (this one isn’t free, but let me know if you’d like a copy for education purposes) detailing the composition of Mt. Discovery lavas. They match the general pattern for Ross Island, so it looks like appearances were a good indication. We have a stratovolcano!

Tomorrow Shelly, Flat Stanley, and I head out for some further training on the sea ice, hopefully the last piece before we can begin work. This training will be the first chance we’ve had to really get away from McMurdo Station and into the environment we came to study, so we are quite excited!