Alyssa Anaya Lab 2 Volcanoes
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Humboldt State University *
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308L
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Geology
Date
Dec 6, 2023
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docx
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Name:
Alyssa Anaya
Lab 2
Explore Volcanoes of the Pacific Northwest
Intro:
The unique aspect of the Cascade volcanoes is that the volcanic chain goes right through North
America’s West Coast of heavily population areas: Vancouver, Seattle and Portland. We know more about
them than any other archipelago in the world because of the threats that they pose to US and Canadian
populations. The range is monitored constantly. The Cascade chain boasts very young volcanoes like
Mount Saint Helens but also very old volcanoes. Their location affords mountain climbers and scientists
alike a ready access to their beauty and their geologic history.
Task:
Go to the website:
https://www.usgs.gov/observatories/cascades-volcano-observatory
Peruse through this website to find out information on the Cascade volcanoes. You may search each
volcano individually by using the map or the list on the right hand side that says “Young Volcanoes in WA,
OR & ID”.
After looking over the images and individual volcanoes, answer the following questions:
1) Of the volcanoes in the Cascade Range between Mt. Lassen in California and Mt. Garibaldi in British
Columbia which has been most recently active?
The most recently active volcano in this area is Mount St. Helens.
2) Which threatens a large municipality?
Mount Hood threatens Portland. Mount St. Helens also threatens Portland, as well as the Yakima area.
Mount Rainier threatens the Seattle and Vancouver area.
3) Which is the oldest?
Mount Adams is the oldest.
4) Which has been historically most frequently associated with glaciation and glacial ice?
The most frequently associated with glaciation and glacial ice is Mount Baker.
5) Why does the volcanic activity stop so abruptly North and South of the limits of the Range?
There is an abrupt stop of volcanic activity at the North and South limits of the Range because this is where
the tectonic plates are creating trenches.
6) Note that Mt. St. Helens and Mt. Adams are offset from the prevailing north-south lineation Rainier,
Hood, Jefferson and Three Sisters. Speculate why their positions vary from the rest of the chain.
I wonder if their positions varying from the rest of the chain because they are on a tectonic plate that is
moving West.
7) Note that the Juan de Fuca
plate is really composed of three
small plates. Name the other two
that are subducting under North
America.
The two plates subducting North
America are the Explorer and
Gorda plates.
8) Based on the shape of the
present plates offshore of the
Pacific Northwest, give prognosis
of what is going to happen to
them in the future as plate
motions continue on their present
courses. In other words, as North
America moves westward, would
we expect the volcanoes at the
extreme North and South to
extinguish at a different time than
the volcanoes in the central
portion of the chain? Explain.
I would expect the volcanoes at
extreme North and South to
extinguish at different times than
those at the central portion. This
is because those at the most
extreme North and South are on
smaller plates.
Application:
Write a summary of the Cascades outlining their origin and an evaluation of the threats that they pose for
people living in their midst.
The Cascades are a range of volcanoes extending from Northern California to southern British Columbia.
These volcanoes originated from the subduction of the oceanic crust sinking beneath North America. The
Cascades is a volcanic zone that features a lot of tectonic and volcanic features. The most recent explosion
was from Mount St. Helen’s and we were able to see just how these eruptions pose threats to the
surrounding communities. Areas near these volcanoes can have eruptions that lead to volcanic ash, property
and infrastructural damage, loss of life, debris avalanches, lahar in rivers. The Cascades began to form
around two million years ago.
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