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.

Minnehaha Falls - In a dry year

Minnehaha Falls is a 53-foot waterfall found near the confluence of Minnehaha Creek and the Mississippi River.  The falls form as the creek flows over the Platteville Limestone caprock to erode the underlying and weaker St. Peter Sandstone.  Between the limestone and sandstone is a thin layer of the Glenwood Shale.  The Platteville, Glenwood and St. Peter are all Paleozoic in age.  An earlier write-up of the geology of the area can be found here.

The month of September 2012 was the second driest month of September on record for the Minneapolis-St. Paul area.  Officially, just 0.30" of rain fell (the driest month of September was in 1882, when 0.27" of rain fell).  Ironically, September 2011 was the third-driest month of September with 0.36" of rain.

The lack of rain has had an effect on Minnehaha Falls, it is nearly dry now.  The source of Minnehaha Creek is Gray's Bay on Lake Minnetonka and in periods of low rain, the outlet to the creek is closed to preserve the lake level.

Without the flowing water, it is much easier to see the sandstone, shale and limestone layers.

See the full size version of the gigapan here.

The Kensington Runestone

Eight Gotalanders and 22 Norwegians on (this) reclaiming/acquisition journey far to the west from Vinland.  We had a camp by two (shelters?) one day's journey north from this stone.  We were fishing one day.  After we came home we found 10 men red with blood and death.  Ave Maria.  Save from evil.  There are 10 men by sea to look after our ships fourteen days journey from this island.  Year 1362.

Incription on the Kensington Runestone.

In September of 1898, the Kensington Runestone was found near the village of Kensington by Swedish immigrant Olof Ohman and his two sons Olof, Jr., and Edward.  The group had been clearing trees on the end of the family plot when they found the runestone.  After cutting the roots of a 25-35 year old aspen, they found a several hundred pound, rectangular stone wrapped within the roots.  It was Edward who noticed the inscription on the stone first.

The Olof family farm where the runestone was discovered is now a county park call Runestone Park.  The location were the runestone was found is marked by a small plaque, just downhill from the United States, Minnesota, Swedish and Norwegian flags.  The Runestone is now displayed at the Runestone Museum in Alexandria, Minnesota.

The Runestone is a rectangular stone that has been obviously split to be that shape.  It is a grey, meta-graywacke glacial erratic.  This rock type is commonly found in the Animikie Basin of East-Central Minnesota and is Paleoproterozoic in age (1,800 to 2,100 million years).

At the time of the discovery, many scholars immediately announced that the runestone was a hoax.  But in 1909, after examining and studying the runestone, Minnesota state geologist, Newton H. Winchell said that "I am convinced that the stone is not a modern forgery....".

Mineral weathering rates provide some evidence that can be examined on the runestone.  Shortly after the discovery, Olof Ohman used a nail to scratch out some of the inscription.  Some of the runes were not scratched out.  The runes that were not scratched out show extensive weathering, pyrite crystals have completely weathered away leaving iron oxide-coated pits.  In comparison to other stones, the weathering of this mineral would have taken more than 23 years, twenty-three years before the stones discovery, Olof Ohman was still living in Sweden.

Comparing the weathering rate of biotite mica in the runestone to the rate found in slate tombstones in a similar evironment, the inscription has been weathering for longer than two hundred years.  The mica minerals in 200-year-old tombstones have begun to fall away, on the runestone, all the mica minerals on the man-made surfaces have weathered away.

There are two options when considering the runestone:
1.  The stone is a hoax.
2.  The stone is real (implying that Europeans reached the interior of the North American continent earlier than commonly thought.

Two books can be read for differing ideas about the history of the runestone, if it is real.
1.  The Kensington Runestone, It's Place in History -  this book describes how the stone could have been carved one day's walk from Mille Lacs Lake in Central Minnesota and how the Dakota Tribe was given/then carried the stone to it's eventually buried location.
2.  The Kensington Runestone - Compelling New Evidence -  this book really lays out the evidence for the stone's authenticity, including the geologic evidence and the linguistic evidence (including ancient Swedish runes that were discovered in the 1900s but are also inscribed on the runestone).

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! 

Roche-A-Cri State Park, Wisconsin

In the book 101 American Geo-Sites You've Gotta See, one of the sites listed for Wisconsin was Roche-A-Cri State Park.  Roche-A-Cri is a 300-foot, bedrock mound that rises above the Central Plain, formerly the floor of Glacial Lake Wisconsin during late-Wisconsin glaciation.  The bedrock mound is comprised of Cambrian sandstones deposited by braided river channels.  Roche-A-Cri translates as "crying or shrieking rock", perhaps a name referring to the hawks that next within the crevices of the mound.

There are numerous vantage points alongside country roads to view Roche-A-Cri.

Reaching the top of Roche-A-Cri requires climbing 303 steps, in two places, resting platforms are provided.

The picture below shows the view visitors can expect while climbing the 303 steps to the top.

The viewing platform at the top of Roche-A-Cri provides great views across Glacial Lake Wisconsin's former floor.

Glacial Lake Wisconsin existed between 18,000 to 14,000 years ago.  This glacial lake formed as the Green Bay lobe approached from the northeast and blocked the early Wisconsin River near the Baraboo Hills.  As the climate warmed, the lake water again found an outlet path through the Baraboo Hills and Glacial Lake Wisconsin catastrophically discharged in a period of a few days to weeks, forming the Dells of the Wisconsin River.

Found throughout the former glacial lakebeds are numerous bedrock mounds, including Roche-A-Cri.  These mounds would have been islands sticking out of Glacial Lake Wisconsin.  All of the mounds have steep slopes that formed by wave erosion.

Interestingly, on the south side of Roche-A-Cri are numerous prehistoric Indian and more recent petroglyphs and pictographs.  An example is found in the picture below, the inscription says:  A.V. Dean. N.Y. 1861.

Minnesota Geology Monday - Mississippi River Headwaters

The Mississippi River is the fourth longest river (2,552 miles) in the world and drains parts of 31 states and 2 Canadian provinces.  The river also has the 4th largest drainage basin in the world (over 1,245,000 square miles), representing almost 40% of the continental United States landmass.  Historically important for early Native Americans and used during the fur trade, today the river is important for tranport of materials via commercial barges.

Expeditions in the early 1800s sought to discover the headwaters of the Mississippi River.  In 1832, led by Native American guides, Henry Schoolcraft identified Lake Itasca as the source of the river.  Schoolcraft named the lake Itasca as a combination of two Latin words, veritas (meaning truth) and caput (meaning head).  The lake is now the namesake of Lake Itasca State Park, which was created in 1891 to preserve the area's remaining virgin pine forests and is Minnesota's oldest state park.

Lake Itasca is at an elevation of 1,475 feet above sea level and is a typical kettle lake found in the area, a result of late-Wisconsin glaciation.  The lake is 1.8 square miles and has an average depth of 20-35 feet deep.  Retention time, the amount of time needed for water to flow from Lake Itasca to the Gulf of Mexico, is approximately 90 days.

The headwaters area was originally swampland.  To give tourists better access, the Civilian Conservation Corps in the 1930s drained the surrounding swamp, dug a new channel and installed a rock rapids.  Many visitors to the area walk across these rock rapids and some subsequently fall into the brand new, Mississippi River.

Minnesota Geology Monday - Dry Waterfalls

At the beginning of August, 1,584 counties in 32 states had been declared disaster areas due to the ongoing drought affecting the United States.  Southern Minnesota has recently received enough rain to move to from the status of 'Drought - Severe' to 'Drought - Moderate' or even 'Abnormally Dry'.  The dry summer months has caused numerous problems, least of which is the drying of the regions waterfalls.

Minnemishinona Falls and the nearby Minneopa Falls are dry, or nearly so.  Both falls occur as water falls over the late Cambrian-aged Jordan Sandstone.  Differential cementation in the sandstone forms the falls, better cemented areas form the top of the falls while while weaker cementation areas are easily eroded at the bottom of the falls.

The picture below shows Minnemishona Falls on June 2, 2012.  Not a high flow rate, but still flowing.

The picture taken on August 4, 2012 shows the falls dry after two months of very little rain.  It is apparently not unusual for this particular waterfall to go dry during late summer months due to the creek's small watershed.

Minneopa Falls is a regional tourist attraction for the beauty of the falls.  The picture below was also taken on June 2, 2012.

Two months later and there is hardly a trickle of water flowing over the falls.

Minnesota Geology Monday - Sioux Quartzite

The most prominent bedrock in southwestern Minnesota is comprised of the 1,700 million year old Sioux Quartzite that extends into South Dakota.  The quartzite ranges in color from pink to purple depending on the amount of iron oxides present.  The quartzite is derived from quartz sand, the source of which was the erosion of the Penokean Mountains, which were located across central Minnesota and into Wisconsin during Proterozoic time.  As the mountain ranges were weathered and eroded, most minerals were broken down into clay minerals and transported away.  The resistant quartz grains were transported south and deposited in a braided stream environment.

Cross beds and ripples found in the quartzite indicate the direction of movement of the flowing river systems as the sandgrains were being deposited.  Most of the cross beds and ripples indicate a southward direction.  Across the border in South Dakota, there are a few locations that have southward dipping cross beds that are found directly beneath northward dipping cross beds.  This potentially suggests that the depositional environment found in this location would have been near an ocean shore under the influence of tides.

Being highly weathering and erosion resistant, the Sioux Quartzite tends to be cliff forming in several locations around the region.  At Blue Mounds State Park, near Luverne, pioneers moving westward used the cliffs as a navigational marker.  The cliffs appearred blue at a distance and were given the name 'blue mounds'.

At Pipestone National Monument, the quartzite also forms cliffs.  The quartzite slowly weathers, primarily via ice wedging along vertical fractures.

During late-Wisconsin glaciation, glaciers also left their mark on the Sioux Quartzite.  Rocks and pebbles embedded in the ice left many glacial striations on exposed quartzite throughout the region.

Early Native Americans also found uses for such a resistant bedrock.  At the Minnesota Historical Site called the Jeffers Petroglyphs, carvings were made into the quartzite beginning 7,000 years ago and continued until recent times.  Carvings at the site include birds, turtles, bison, thunderbirds, weapons and a great number of other objects.  The site most likely represents religious illustrations of impartant aspects of the lives for these earlier Native Americans.

The Sioux Quartzite has been (and still is) used widely as both dimension stone and aggregate.  Modern quarries of Sioux Quartzite can be found as far east as New Ulm and extend west into South Dakota.  Early quarries used for these purposes include this late 1880s quarry found near Luverne.

Many towns in the region have buildings made out of the resistant Sioux Quartzite, including the Rock County Courthouse.

Minnesota Geology Monday - Pipestone National Monument

Pipestone National Monument is located on US Highway 75, approximately 25 miles north of Interstate 90.  The monument focuses on how Native Americans have quarried catlinite out of the region to be carved into pipes or other structures.  Catlinite is a metamorphosed mudstone with a fine-grained texture and it can be easily carved.  Due to the presence of iron oxides, the catlinite is deep red color.

At the entrance to the park office is the first stop, a series of granite boulders called the Three Maidens where Native Americans would leave offerings before proceeding to the quarries.  Native Americans realized that these boulders did not match the local bedrock and thus were significant spiritually.  These glacial erratics were transported from the Ortonville, MN area and broken into many pieces by the process of ice wedging.

Prior to the late 1880s, there were 35 pieces of rock containing petroglyphs that had been placed at the Three Maidens location.  These were removed in 1888 or 1889 because some of the petroglyphs had been defaced, but were returned to the monument in the mid-1900s.  These petroglyphs are now on display at the visitor center.

Bedrock in southwestern Minnesota is the 1,700 million year old Sioux Quartzite.  The quartzite ranges in color from white to pink to purple and derived from quartz sand.  The source location of the sand grains is the erosion of the Penokean Mountains which were located across central Minnesota and into Wisconsin during Proterozoic times.  Cross-beds and ripples found in the quartzite indicate the direction of movement of the flowing water as the sand grains were being deposited.  The majority of the cross-beds and ripples suggest a southward direction of flow.  The Sioux Quartzite correlates well with other quartzites in the region, including Wisconsin's Baraboo Quartzite.

Because the quartzite fractures along vertical joints, it tends to form cliffs.  Though weathering of this nature has also formed feature known locally as the Old Stone Face.

Or this structure known as the Oracle.

Because the quartzite is erosion resistant and cliff-forming, a creek has developed a waterfall in the park over the escarpment called Winniwissa Falls.  It must be one of the very few waterfalls present in southwestern Minnesota.

Further south of the waterfall, the escarpment continues, at the base of the escarpment are evidence of plunge pools and scour holes.  Looking west of the escarpment (the direction the creek flows) there appear to be dry channels.  As the glaciers where melting in the late Pleistocene, meltwater would have been pouring through the area creating a much larger waterfall.

Native Americans continue to quarry the catlinite in several quarries like shown below.  The park service needs to pump water out of the quarries before work proceeds.

Quarrying would have (and still does) as demonstrated by one of the park's informational signs.  The letter A represents the catlinite, B is the overlying Sioux Quartzite, C is the soil layer, while D is the rubble pile created by removing the Quartzite and soil.  Since the quartzite and catlinite layers dip be 5-10 degrees to the east, more and more quartzite must be removed in order to reach the catlinite layer.

The park service has cleaned up one of the older quarries for tourists to enter.  At the bottom of the quarry face is the catlinite layer, the layer is approximately 10-15 inches thick and much softer than the overlying Sioux Quartzite.

Because of the cultural and geological significance, Pipestone National Monument was recently included as one of the 101 American Geo-Sites You've Gotta See in the book by Albert Dickas.