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Minnesota is understood for its flat grasslands and rolling prairies, however one space of the state diverges from the norm.
The dramatic bluffs overlooking the Mississippi River in southeastern Minnesota draw many guests to this space, together with nature lovers searching for biking, canoeing, and climbing trails.
Amanda Lewandoski loves driving on the freeway. 61 and admire the cliffs. She puzzled how they’d arrived.
“Typically you’ll be able to see layers on the cliffs and I am actually curious to know what all of this implies and the way lengthy this has all been occurring,” she stated. Lewandoski submitted the query to Curious MinnesotaStar Tribune’s group reporting undertaking fueled by questions from readers.
The brief reply is that the dearth of glacial exercise on this nook of the state over the last ice age created a singular topography that was later amplified by subsequent flooding from melting glaciers elsewhere.
The good flattening
Glaciers performed an essential function in shaping Minnesota’s topography, regularly altering the panorama over hundreds of thousands of years.
Glaciers got here and went in Minnesota throughout many ice ages. In accordance with Dylan Blumentritt, professor of geosciences at Winona State College, these gargantuan lots of ice slowly moved throughout the plains and reshaped the land round them, smoothing the bottom like a bulldozer.
“They fill in low areas, they erode excessive areas, and so they flatten the panorama,” Blumentritt stated.
However glaciers did not contact southeast Minnesota over the last ice age greater than 10,000 years in the past, creating extra different topography there.
This allowed rivers to kind in what is named Bluff Nation or Driftless Space. These rivers finally stuffed with large quantities of melted glacial ice, which carved out bigger valleys all through the Mississippi and Minnesota river system than different waterways within the state.
“As glaciation continued north, Lake Superior grew to become so stuffed with meltwater that sediment-free water overflowed into the Mississippi through the St. State of Winona, Calvin Fremling, in a 1984 report on Lake Winona. “The sediment load of the Mississippi River was thus diminished and it was capable of export sediment quicker than its tributaries introduced it in.”
These deep cuts have occurred over 1000’s of years. Drivers like Lewandoski can see the stone layers within the cliffs in addition to the terraces, like large steps, main right down to the river. These are the results of water with out sediment digging into the earth.
This erosion has uncovered layers of historic rock.
On the backside of the valley is sandstone from the Cambrian Interval greater than 500 million years in the past, when the land that shaped Minnesota was barren and with out a lot vegetation to carry the dust in place. As vegetation grew and water lined after which receded from the land, several types of rock have been shaped, resulting in the shale, mudstone, dolomite and limestone that make up the cliffs.
Pure erosion continues to form the cliffs, however human exercise has accelerated the adjustments. It’s believed that human exercise over the previous 200 years has modified the construction of the cliffs at a quicker fee than traditional.
It began when Europeans settled in Minnesota. Within the 1850s, when everlasting settlers arrived within the Driftless space, they lower down timber and raised cattle on the cliffs. The extraction of vegetation holding soil and rock in place added large quantities of sediment to the underside of river valleys. This led to extra air pollution within the rivers, in addition to extra soil erosion close by.
“We name it legacy sediments,” Blumentritt stated. “It is the legacy left by these settlers. They did not know it will have lasting results, nevertheless it did.”
Blumentritt will work with geologists from the College of Minnesota and Minnesota State College, Mankato in an upcoming examine to see how settlers affected the Whitewater River Valley within the southeastern portion of Utah. State – a tributary of the Mississippi.
Different geologists have studied cliffs throughout the state lately, partly to see how local weather change and more and more extreme climate are affecting the panorama.
Geologists have been requested to look at river valleys following a 2013 landslide at Lilydale Regional Park in St. Paul that killed two younger college students. The researchers concluded that the landslide was probably caused by latest rains and soil erosion, nevertheless it led native and state officers to authorize an enormous landslide survey in 2018.
This examine discovered that components of the state, such because the Minnesota River Valley, have been far more liable to landslides and geological adjustments because of an absence of vegetation holding the soil in place. This example is exacerbated by extra violent episodes of rain because of local weather change.
Which implies there will likely be extra alternatives for bluffs to vary drastically sooner or later.
If you want to submit a Curious Minnesota query, fill out the shape under:
Learn extra curious tales from Minnesota:
Who dug the sandstone caves along the St. Paul River?
Is Little Lake Itasca in Minnesota the true source of the Mississippi River?
Is it safe to swim in the rivers of the Twin Cities, or are they too polluted?
What did the topography of the Iron Range look like before it was mined?
Does Minnesota really have the “oldest rock in the world”?
Should Minnesota be considered part of the Midwest?
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