GEOG 1301 Unit 7


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Unit 7: The Lithosphere



A.  Read the following selections from the Margin Notes by clicking on each link.


B.  Watch these presentations. When you click on one of the links below, a new screen will pop up. Use the scrollbar on the side of the new screen to navigate. You need Adobe Reader to view PDF files.HELP MESSAGE


C.  (Optional) Read the following chapters from the textbook.

Chapters 12 - 20


D1 Print the Required Links documents below and include them in your field manual. (See Field Manual Protocols, available as a download on the Unit 8 page.)


D2. The following Optional Links will help you do better in your course but they are not required.


E.  Activity #4: Mystery of the Mega Volcano (10 points)To Do Note

Super volcanic eruptions are extremely large eruptions that produce at least 1,000 cubic kilometers of magma and pyroclastic material (a hot, dry, fast-moving mixture of ash, pumice, rock fragments and gas).

These eruptions could destroy virtually all life within a radius of hundreds of kilometers from the site and could bury areas as far away as 1,500 kilometers in meters of ash. Very large-scale explosive eruptions of this type produce calderas, large depressions formed by the collapse of the summit or flanks of a volcano.

Watch A Supersized Volcano.

Watch Blasts from the Past.

Volcanic ash consists of rock, mineral and glass fragments smaller than two millimeters in diameter. Ash is formed by the catastrophic drop in pressure on magma brought about by the volcanic eruption (breaking up the volcanic edifice results in atmospheric pressure inside the volcano). This causes gases in the magma to expand violently, fragmenting the magma into tiny pieces, which instantly solidify on ejection into the atmosphere (lower temperature compared to magmatic temperatures).

Ash from a particular volcano has its own unique characteristics, much like a person's fingerprints. These characteristics include chemical composition, and the size and shape of crystals and glass shards. They can be used to determine not only the particular volcano that produced the ash, but the particular eruption from that volcano as well.

The characteristics, along with the age of the ash, help scientists identify the source of material. Volcanic rocks are typically divided into four basic types basalt, andesite, dacite and rhyolite according to the average concentration of major compounds in the rock. These compounds include silicon dioxide (SiO2), titanium dioxide (TiO2), aluminum oxide (Al2O3), iron oxide (FeO or Fe2O3), manganese oxide (MnO), magnesium oxide (MgO), calcium oxide (CaO), sodium oxide (Na2O), potassium oxide (K2O) and phosphorous pentaoxide (P2O5).Michael Voorheis

In 1971, Michael Voorheis, a paleontologist at the University of Nebraska State Museum, made a startling discovery at a farm in northeastern Nebraska. He uncovered the bones of 200 fossilized rhinos, together with the prehistoric skeletons of camels, lizards, horses and turtles. They had been killed millions of years ago by suffocating amounts of volcanic ash (the site later became known as Ashfall). But there are no volcanoes in Nebraska, nor had there ever been. In fact, there are no volcanoes in the continental US east of Colorado. So where did the ash come from?

I'm giving you the responsibility for solving a mystery: Which super volcano killed the creatures found in Nebraska's Ashfall Fossil Beds 10 million years ago? Your job: Use clues from the scene to hunt down the volcano responsible.


Use the Volcanic Identification - Data from the Ashfall Fossil Beds data to identify the type of ash at the Nebraska Ashfall Fossil Beds site and the type of eruption and volcano that might have produced it.

Now that you have some idea of what kind of volcano was responsible for the Ashfall Fossil Beds, you need to decide which of 8 possible volcanoes is the most likely.

You have been provided with three sets of real volcanic data for the 8 suspect volcanoes -- (1) Location, (2) Description and (3) Ash Composition. Consider the three data sets in the order given. For each of the three data sets, you must analyze the information and -- based on that data -- eliminate the volcanoes you think least fit the profile for the Ashfall event.

After you analyze each data set, answer the questions at the end of that data set and record your results in the Volcano Suspects Table before continuing to the next data set.

After you have analyzed all three data sets and filled out your Volcano Suspects Table, identify your main suspect and answer each of the six questions in the last section. Your answers should be thorough, specific, include relevant concepts from the course material and be free of spelling and grammar errors. In your answers, make specific and detailed connections to course content.


Activity Submission Instructions

By the deadline shown in the Course Schedule on the main page of the syllabus:
  • Send a summary of your investigation results, including your answers to the six questions and your completed Volcano Suspects Table, in the body of a new email to

  • Put only your name and Activity #4 at the beginning of your email.

  • Be careful to use the correct subject line.

  • Late summaries will lose one point per day late, including weekends and holidays.



Copyright 1996 Amy S Glenn
Last updated:   02/14/2018   0130

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