The Lower Carver Rapids on the Minnesota River

Historically, the upper and lower Carver Rapids on the Minnesota River stopped steamboat traffic up the Minnesota River during times of low water.  Having the water level on the river low enough to expose the rapids had been described as a rarity, though the rapids have been exposed for much of the past year due to dry conditions found throughout the Minnesota River basin.  My first trip to the rapids took place last fall when the river was at 5.37 feet, according to the closest river gauge, and can be re-visited here.  Because of the lack of snow last winter and continued dry or drought conditions this summer, the river level has continued to fall to a current level of 3.66 feet.

The picture below shows the lower rapids a year ago from the southern bank of the Minnesota River.  Though the upper rapids were exposed at the time, the lower rapids were seemingly just below the surface of the water.

Ten months later, with the continued drop of the Minnesota River, the lower rapids have been exposed.  The picture below was taken from the northern bank of the Minnesota River.

The rapids are created as water flows over the Cambrian-aged Jordan Sandstone.  The bedrock here is one of the very few locations of exposed bedrock in Carver County, Minnesota.

Below is a 1.15 gigapixel image of the lower Carver Rapids taken from the northern bank of the Minnesota River.
To see the full size gigapan, click here.

My First Attempt(s) at Gigapans

Over the summer I acquired at Gigapan EPIC 100 with the goal of using gigapans within my Earth Science classroom.  The idea of placing students at an outcrop or location, even though it may be hundreds of miles away, is intriguing.  Ideally, many of the gigapans used in the classroom would have a Minnesota focus, that way students would be able to visit locations in the state virtually.  Many times, individual rock samples cannot tell the complete story that the entire outcrop can, and that is one reason why gigapans are coming to my classroom.

I've put together a list of some gigapans that focus on different parts of Minnesota's geology and have shown these informally in the classroom at various times in the past.  So many of my students have been introduced to gigapans and some browse the gigapan website on their own time.  

Each fall, we take the entire 8th grade class (198 students this year) on a field investigation to three different locations in or near the Minnesota River Valley (you can read about last years trip here), with the goal of being able to make observations about how the valley formed.  This was an obvious place to start my gigpan experience, some of these went very well, but there were certainly lessons learned.

The first gigapan was shot just beneath the highway bridge over the Minnesota River near Blakeley.  We stop here to get an idea of how big the valley is and how little of the valley the river occupies.  To view the gigapan online, click here. 

The second gigapan was at the Rush River County Park, shot from a rocky point bar.  This was basically shot to allow the sun to rise a little higher in the sky to set up the next gigapan.  The gigapan can be found online here.

The third gigapan was the one that I wanted the most for the classroom, but it's also the one where the most mistakes were made.  First the batteries on the camera died, then the memory card of the camera got full, missing a picture or two before I realized it (of course I was using the 1 GB card, not the 16 GB card that I have).  The mistakes are correctable and I'm currently making time in my schedule to get back to the site to make a better gigapan.  

Obviously, you can see the missing picture, which threw the rest off slightly.  The site here is continually eroded by the Rush River and exposes at least three distinct glacial tills, the source of the rocky point bars.  The gigapan can be found here.

So the learned are:

1.  Use the bigger memory card.
2.  Don't forget about the batteries.
3.  Keep practicing.

If anyone has any ideas about how they are using gigapans in the classroom, I would love to listen! 

Minnesota Geology Monday - MN River in Flood

The Minnesota River occupies the former channel of Glacial River Warren, one of the outlets to Glacial Lake Agassiz.  Because the Minnesota River is much smaller than the channel in which it flows and is too small to have carved the channel, it is considered to be an underfit river.  Flooding in the river valley is common when conditions are met, namely a wet spring coinciding with a fast snowmelt.  During periods of flooding many of the bridges over the river are closed due to either water over the roads approaching the bridge or stresses placed on the bridge themselves.

Due to the relatively flat topography of the river valley (largely due to Glacial River Warren), during periods of heavy flooding, large portions of the valley are covered by water.  All of the pictures in this post were taken during 2010.

For many locations and cities along the Minnesota River, the spring flood of 1965 still holds the record for the highest level ever seen of the river.

Because of the nature of the 1965 flood, many cities built better flood protection devices like dikes with the help of local, state, and federal money.  Along with the dike that encircles the city of Henderson, the city has two flood gates that are closed when the river reaches a height of 734 feet.

The highest recorded river level in Henderson was September 28, 2010 at 740.08 feet (http://water.weather.gov/ahps2/hydrograph.php?wfo=mpx&gage=henm5).