Monday, October 29, 2012

The Geology of the Black Hills

Image Courtesy of Beth Steinhauer, Black Hills National Forest
(Forest Service of US Department of Agriculture) under Public Domain
Many of you have been out to the Black Hills. If you haven't (or if you can't remember what it is like), visualize the following scenario:
As you drive west from Rapid City, you notice a jagged stretch of sandstone peaks called the Hogback Ridge. After a short descent from those sandtone peaks, you come to an area comprised of another sedimentary rock, red shale, which makes a "Racetrack" around the Black Hills. If you keep driving west, there is a gradual incline made of limestone. This limestone formed 100-500 million years ago, from the shells of ancient marine animals. (Yes, we are still in the Black Hills of South Dakota.) Keep driving still, past this limestone plateau, and you will see the Central Crystalline Core of the Black Hills. This area is made of schist (a metamorphic rock) and granite (an intrusive igneous rock) that have aged for up to 2.5 billion years. The apparent color of this Central Core and the groves of Ponderosa Pine gave this area its name, the Black Hills. You might want to get out of the car and take a hike up to Harney Peak, the highest peak in between the Rocky Mountains and the Alps of Switzerland.
What are the events that led to the formation of these Black Hills? Why does it look the way it does? Like geologists, we will explore these questions today.

  1. Write a summary of how the Black Hills formed. What are the events that led to their formation?
  2. Would the Badlands exist if weathering/erosion had not taken place? Why/Why not?
  3. The major uplift of the Black Hills occurred 70 million years ago. What do you think that area of South Dakota looked like 40 million years ago? What do you think the Black Hills and Badlands will look like in another 40 million years?

18 comments:

  1. 1. A great mass of molten rock began to rise from deep within the earth’s crust. As this mass cooled, it formed the granite which is now the core of the Black Hills. The molten rock cooled unevenly, forming both blocks of relatively fine grained rock and, more commonly, blocks of coarse grained pegmatite.
    2. No, they would not be the same because the sediment that moved from the Black hills went to the Bad Lands and created the Bad Lands so the Bad Lands wouldn't be there if the sediment hadn't moved.
    3. The Black Hills were probably taller back then than they are now. In another 40 million years, the Black Hills will be smaller because they keep getting smaller over the years.

    ReplyDelete
  2. 1. Schist, Granite, Limestone, Red Shale, Sandstone, Uplift.
    2. No because the weathering is what formed the Badlands.
    3. 40 million years ago - It probably still looked a little like it does now, but just not as extreme. 40 more million years - It will probably just weather a ton more and maybe it won't even look the same as it does now.

    ReplyDelete
  3. The black hills were formed by rocks compressing on top of each other and by coming in contact with molten rock or lava. After there were so many layers the molten lava wanted to get out. The only way out was up so the lava pushed up causing an uplift. the uplift split the rocks in half and mixed the layers up.

    ReplyDelete
  4. 1. Uplift of magma lifted up the rock layers, Then they got arounded over millions of years. TADA!!!

    2. No the weathering on the Black Hills moved its rock to the badlands forming them.

    3. A magma push, MOUNTAIN!. Flat then BOOM huge mountain. Badlands will b taller and the Black Hills will be very small!

    ReplyDelete
  5. The Black Hills were formed by layers of rock. First igneous rock called schist and granite formed the core. Next three kinds of sediment rock piled on. The reason they popped up from the ground is because of an uplift.
    No. The Badlands are the sediment rocks that have eroded from the Black Hills, no Black Hills, no Badlands
    40 million years ago it was a taller formation.
    40 million years from now it will be shorter.

    ReplyDelete
  6. 1. First uplift pushed the ground up and made a mountain. Then they started being affected by weathering and erosion. Slowly rocks were worn away and now they're all at different elevations.

    2. No, because the weathering wouldn't have carried all the stuff from the Black Hills over to the Badlands.

    3. A big lump of rocks with a little bit of weathering.

    In another 40 million years I think they will be a big trench thing where the red shale is worn away a lot. The Granite will probably be like a big tower.

    ReplyDelete
  7. 1. About 1.6 million years ago a great molton rock began to rise from deep within the earth’s crust. as it cooled. it formed the granite which is now the core of the Black Hills. The rock cooled unevenly forming both blocks of relatively fine grained rock. a large block of fine grained rock formed the upper portion on Mt. Rushmore.

    2. No, because the weathering is what transferred materials there. And Erosion moves the rock around and it needs that to be there.

    3. I think that SD wasn't as rocky 40million years ago. In 40million years, i think the badlands will be covered in ash, and lava from Yellowstone erupting.

    ReplyDelete
  8. They were formed 70million years ago. The melted magma cooled and then layers apon layers of different kinds of rocks. No, it needs the wind and other weathering components to carve it out. It probably looked like now but the mts. weren't as big. I think the mts. will start eroding and get smaller.

    ReplyDelete
  9. -The Black Hills were formed were formed through lots of erosion and finally uplift. It started with a layer of schist/granite, limestone, red shale, then sand stone. As the layers grew, the material became stronger and stronger.
    -I don't think they would exist without the uplift. It would just be a flat plane.
    -I think that 40 million years ago it looked quite ragged but not as different as it does today. I think in another 40 million years it will be extremely sharp/pointy in all areas and there probably won't be any flat plateaus.

    ReplyDelete
  10. The Shishts was first then granite,limestone, red shale and last sandstone.The sandstone, red shale and limestone eroted then the granite and shits now shows.
    No because the arousion from the black hills went into the badlands.
    It looked like a taller black hills with sandstone on the top, in 40 million years it will be mostly gone and it will be flat like the rest of SD@@@@@@@@@@@

    ReplyDelete
  11. 1. The Black Hills started as Schist(funny word) and Granite. It started underwater(crazy!!!). After awhile the heat and pressure made it big and it popped out of the water. Later on(like a few million years or so) other rock started to form creating the Black Hills.

    2. I think the Badlands would still exist but they wouldn't be as awesome as they are now. They probably would just be a big hill. Lack of color. Lack of wonderfulness.

    3. I think the area of South Dakota was more rocky and hilly and bumpy and such. In another 40 million years I think that the Black Hills will be close to flat and the Badlands will be all gone from the wind blowing it away.

    ReplyDelete
  12. 1. They formed when molten rock began to rise up from deep within the earth's crust. Then limestone formed on top of that, then red shale, then sandstone, which formed the Black Hills.

    2. No, because the sediment that makes the Badlands comes from weathering/erosion of the Black Hills.

    3. 40 million years ago, the Black Hills will have gotten somewhat shorter as the top layers of sediment began to crack and the granite/schist core continued rising up. In 40 million years, the Black Hills will probably be a short mountain of granite and schist with some limestone, red shale, and sandstone around it.

    ReplyDelete
  13. 1. Around 1.6 billion years ago, molten rock rose from the earth's crust and formed granite, the core of the Black Hills. 500-1000 million years ago rocks formed the sides of the Black Hills, most of them were limestone. Red Shale was deposited on on the Black Hills. Then Sandstone was also deposited. 70 Million years ago the Black Hills began to uplift. The crystalline core began to crack and erode away. The uplift is still going on.

    2. No because all of it was created by weathering and erosion.

    3. It was not as big 40 million years ago and it will get bigger in another 40 million years.

    ReplyDelete
  14. 1.The granite and schist formed first. After that, limestone was formed from the bones of marine animals.Then the red shale formed, and finally, the sandstone formed most recently. they were all on top of eachother.

    2.No because the uplift from the black hills made the rock from the badlands move, forming the jagged peaks that are still being eroded.

    3. I think that 40 million years ago the Black hills were taller than they were today. in the future they will be shorter than they are today.

    ReplyDelete
  15. 1) Granite and schist formed and then limestone formed on top of that, then red shale and sandstone. Then uplift happened and the Black Hills were raised.

    2) The Badlands would not have formed without weathering and erosion. The sediment moved down from the Black Hills to form it.

    3) I think it will look very different, possibly even higher up.

    PDP

    ReplyDelete
  16. 1. First the schist, granite, limestone, red shale, then sandstone was layered where the Black Hills was. Then uplift happened and moved all layers up to a elevation of 15,000 feet. Because of the least resistance to weathering, the others layers fell, and the entire thing moved down to the now elevation of 7000 feet.
    2. NO because the sediment that moved from the Black Hills went to the Badlands and formed the Badlands.
    3. I believe that the Black Hills were super tall and there wasn't as much eroding-ness. The Black Hills in 40 million years could be much flatter.

    ReplyDelete
  17. 1. Molten rock from deep inside the earth rose and cooled unevenly causing both fine grained rock (fast cooling) and coarse grained pegmatite (slow cooling) to form.
    2. Yes because it formed not because of weathering and erosion but thats why it looks the way it does now.
    3. The mountains were probably taller 40 million years ago and will be shorter still in another 40 million years.

    ReplyDelete
  18. 1. Molten rock from deep within the earth cools unevenly causeing finely grained rock and coarse grained pegmatitie to form.
    2. Yes because Its not formed solely of weathering and erosion.
    3. Mountains were most likely taller last 40 million years and they will be shorter in another 40 million.

    ReplyDelete