Tag Archives: geomorphology

Geomorphology extra: winter on Lake Michigan

I went as a teaching assistant on field trip for an environmental studies senior seminar class this past weekend, and we winter camped at Sleeping Bear Dunes National Lakeshore near where the Platt River enters Lake Michigan. The purpose of the field trip was to get students into an unfamiliar and slightly uncomfortable setting right away at the start of the semester to spend some time getting into the practice of having good and difficult discussions. There’s nothing like setting up camp in the fading light of a Michigan winter evening to build the sort of trust and mutual reliance that make for such discussions.

It was certainly a good trip, and I guess we’ll see soon if it succeeded or not. We had beautiful weather with temperatures in the 20s and lots of sun, and a mile-long walk through a couple feet of snow to the lakeshore was an unexpected treat. I’m not sure you’ve really lived if you’ve never seen a huge body of water frozen over, and Lake Michigan in the winter has lots of sweet ice formations (check out National Geographic’s photo of the day from Jan. 21 for evidence).

In addition to ice volcanoes and shelf ice, there were some great niveo-aeolian sand deposits (think of it as an ordinary dune landscape plus snow).
Where sand was deposited on snow,  I stepped expecting to stand on relatively solid ground, only to fall through half a centimeter of sand and into much deeper snow. But it was even cooler to see how the snow was eroded from the windward side of the foredunes and deposited on the slipface. It’s exactly the process that shapes sand dunes when there isn’t snow, but the presence of the snow and the color contrast with the sand made it so nicely visible:

There were a few geology majors along who could explain some of the formations to me better than I understood them myself, and it was a real gift, that trip to the lake. I had wanted to see some deer on the walk, but instead I got a lesson in coastal geomorphology. It wasn’t what I was expecting or hoping for, but as every geology student (and fan of the Stones) knows, you can’t always get what you want.

Star Dune Enterprise

This week’s LotW is the star dune. Like yardangs, star dunes are large scale aeolian landforms, but they’re depositional rather than erosional, and they’re composed of sand rather than sedimentary rocks. This is not the best picture, but it’s open source (from Wiki Commons), which is a good thing.

I live in a very duney landscape (the east coast of Lake Michigan) but I didn’t realize how many different shapes and sizes of dunes existed until I took a class from a coastal dune specialist. Star dunes don’t form on coasts—they’re more common in giant sand seas like those found in Algeria or Namibia—but they are awesome.

Form: 3 or more sharp-edged ridges extending from a single high pointed peak.
Composition: sand.
Formation: formed in environments with low vegetation and lots of sand where the wind blows from multiple directions. They grow up rather than out and can be some of the largest dunes in existence.

Landform of the Week: Yardang

I’m enjoying all of my classes this semester, but it seems that geomorphology has really captured my imagination. So much so that I’ve decided to start a landform of the week feature for the duration of the semester. Wednesday, colloquially known as ‘hump day’ as it is, seems like an appropriate day for a landform feature, and our inaugural landform—THE YARDANG!—does indeed resemble something of a hump. The below picture is from Wiki Commons and shows a yardang near Meadow, Texas.

A yardang is an aeolian landform (meaning that it’s formed by the wind), it’s fairly large scale, and it’s the result of erosion. Yardangs can usually be found in groups, because basically, you’ve got strong winds carrying abrasive sand chipping away at a surface of smaller, more cohesive sediment until the surface gradually erodes into distinct hills. They’re quite common in deserts and can actually take a variety of shapes. One of the more famous yardangs in America is Window Rock in Arizona, which has a hole worn through it. The Oxford English dictionary informs me that the name yardang (you know I’m going to use that in Scrabble) comes from the Turkish yar, meaning steep bank.

So there you go, I’m incorporating a bit of Turkish from my history thesis too.