Supervolcanic 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 at
www.pbs.org/wgbh/nova/megavolcano/supe-flash.html.
Watch Blasts from the Past at
www.pbs.org/wgbh/nova/megavolcano/blas-flash.html.
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).
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 supervolcano 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.
[Note: The data sets and
table referred to below are on the Activity Resources page.
The link for that page is at the top of this page or you can use the individual hotlinks given
in the instructions.]
A. 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.
B. 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 suspect 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.
C. 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.
In your answers, make
specific and
detailed connections to course content.
Please be careful
to use correct spelling and grammar.
D. 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
dramyglenn@earthlink.net.
-
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. (Although I do take
late assignments, I do not take assignments past the end of the
semester. Check the Course Schedule on the main page of your
syllabus for the final date I will accept assignments.)
READ THE FOLLOWING SECTIONS FROM THE MARGIN NOTES.
