Plate Tectonic - Hazards (6)
Pre Lab 

  • Comparing earthquakes in Alaska and Hawaii.
  • Exploring the Modified Mercalli Scale.
  • converge
  • Mercalli Scale
  • worksheet
  • map with Pacific "Ring of Fire"

Students compare earthquakes using the Modified Mercalli Scale.

Earthquake rupture along a fault line


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.

  1. 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."
  2. Have the students complete the worksheet.
    1. Which state had the most earthquakes? ALASKA
    2. Which state had the strongest earthquakes? ALASKA
    3. 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.

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