Monday, July 9, 2012

Aerial Geology #1: First Contact

At last, I've used my powers of flight to make a geologic observation from the air. This is an exciting first to my blog, and I look forward to more of the same.

This last weekend I flew down to a Fly-in/Drive-in breakfast and air show that is held every summer in Winona, Minnesota. For the few years I worked, went to school, and learned to fly there, I would volunteer for this event and it was always a thrill. I've missed the last two, on account of being in Missouri for grad school, so it was great to be able to fly there from the Cities. Also, it was nice to get in some cross-country flight time. I took the trusty Cessna 152 I've been hopping around in lately.

My trusty steed, 100x stronger than the average horse

I learned to fly along the Mississippi River, so it was great to re-visit my roosting grounds. And of course, you can't beat the view.

Composite photograph of view from the Cessna 152 flying up the Mississippi River;
stream valleys (left view), Mississippi River and Highway 61 (forward view), and Lock and Dam #5 (right view) 

Now, for the geology. On the way back to the Cities I noticed a decent sized quarry down amongst the little stream valleys.

Now, I've seen quarries from the air before, but after looking closer (especially in the photograph), I noticed something obvious: there were two distinct formations in that outcrop; an orange lower unit and a buff-gray upper unit.

Outcrop near Winona, Minnesota, showing Cambrian-Ordovician boundary as the sharp contact between the Jordan Sandstone (orange, lower unit) and Oneota Dolomite (gray, upper unit)

I think any other place and I would have just dismissed it, but that combination of rock colors in that sequence, and for this region, represents a geologic contact that is well-known to every geologist and geology student in the area. The bottom orange-tinged unit is the Jordan Sandstone, and the upper gray unit is the Oneota Dolomite. The contact is the Cambrian-Ordovician unconformity.

Stratigraphy of Minnesota

All geology students recognize the Jordan Sandstone because it tends to break easily and stains your hands and clothes a rusty-orange. There is a large outcrop of rock that students are brought to which we just call "Homer", and the Jordan Sandstone is part of the sequence of rocks exposed there.

Roadside geology at Homer Ridge; me (left), fellow geologist Laura, and Jordan Sandstone (right)

The Oneota Dolomite, above the Jordan Sandstone, is known around the area for making up the resistant caprocks for the bluffs. Around Winona everyone sees this formation all the time as Sugar Loaf, the pinnacle of rock seen from almost anywhere in the city, even at night (they light it up), as a remnant from quarrying.

Sugar Loaf bluff, Winona, Minnesota

Thursday, July 5, 2012

Aerial Geomorphology #2: Twin Cities Flight

After moving to the Twin Cities I recently began flying out of Anoka County-Blaine and Flying Cloud Municipal airports. I had my biennial flight review in a Cessna 172, and also got checked out in a Cessna 152, which was a bit of a change for me, since almost all my single engine time is in a Piper Warrior II. The one advantage of the Cessna 172 and 152 is the high-wing design allows for better downward visibility, and therefore, better aerial photography. In the spirit of my blog, I took a friend up flying the other day, both because she had never gone flying in a small plane before, and also to get some nice pictures of local geomorphology.

The plane

The pilot

The photographer

The plan of the flight was to take off from Anoka and fly east towards the St. Croix River and back while checking out the many lakes and streams along the way.

Flight planning

This route took us over lots of the smaller lakes, and it seemed like everyone with a boat had it out that day. It had been really warm lately, so I don't blame them.

Center City, Minnesota
South Center Lake (bottom half), North Center Lake (top half), and Little Lake (far back, right)
After flying around my friend looked down and said, "Hey, meandering stream!". This turned out to be the Sunrise River, and it meadered quite a bit, even had some cutoff meander bends. Aerial geomorph gold! We followed it for a while as it flowed into some larger pools which became streams again.

Sunrise River, complete with meander cutoff bends

Sunrise River, with good examples of meander cutoff bends
Sunrise River, Sunrise River Pool #1 (left), Mud Lake (background)

The Sunrise River flowed into the Pool, where it branched and part of it went southward and another part of it went westward. We followed the westward branch, which eventually flowed into Martin Lake. All along the way the river had lots of meander cutoffs.

Sunrise River flowing into Martin Lake

It's nice to be flying again, and after years of geology education I love to notice the interesting landforms and stream types. Time to plan some other flights!