BACKGROUND:
Hawaii and Alaska both have volcanoes and earthquakes.
The active Hawaiian volcanoes and earthquakes are concentrated on the big
island of Hawaii. Volcanic activity decreases progressively with each island
further to the northwest in the chain. The age of the volcanoes increases in
the same direction. Hawaii is not on a plate boundary, but in the middle of
the Pacific Plate.
The Hawaiian volcanoes are not explained by plate
tectonics, but as "a hotspot." A hotspot is a relatively
stationary plume, or rising column, of magma in the Earth’s mantle, below
the plates. When this rising plume strikes the bottom of the Pacific Plate,
its melts its way through it. Some of this magma erupts, building the
Hawaiian Islands. New volcanoes form as the plate keeps moving over the
hotspot. This is why the volcanoes get older to the northwest; they formed
in the past, when that part of the plate was over the hotspot. They have
since been moved away.
The southern part of Alaska has volcanoes because it
is at the converging plate boundary between the Pacific Plate and the North
American Plate. At this boundary, the Pacific Plate is subducting into the
mantle. As it subducts, it melts, generating magma that rises to form the
volcanoes. Large earthquakes occur as the plate subducts. The volcanoes and
earthquakes caused in Alaska are thus explained by the theory of plate
tectonics.
In this exercise, the students will use the Modified
Mercalli Scale to determine whether Hawaii or Alaska has stronger
earthquakes. They will learn that Alaska has bigger earthquakes. This is
because it is at a converging plate boundary, whereas
Hawaii is not.
PROCEDURE:
- Have the students examine map with earthquakes and
volcanoes plotted on the map. Have them compare where the Hawaiian
Islands and Alaska fit into the global pattern of earthquake activity.
They should realize that Hawaii is more isolated, where Alaska is part
of a larger zone called the Pacific "Ring of Fire."
- Have the students complete the worksheet.
ANSWERS:
- Which state had the most earthquakes? ALASKA
- Which state had the strongest earthquakes?
ALASKA
- Color in red those areas that you feel are very
dangerous and hazardous places to live. Why are those areas so
dangerous?
The most hazardous and dangerous areas are found in Alaska. Those
areas are dangerous because they lie along a converging plate
boundary.
