Horizontal Extension (Grades 9-12)

As the volume of magma in the reservoir increases, the summit of the volcano inflates. In addition to the increase in tilt, inflation is also indicated by an increase in distance between two points on the summit of the volcano. The graph in activity 7 shows the changes in the distance between the same two points on the rim of Mokuaweoweo Caldera over a 20-year period (Lockwood and others, 1987). The two points are the summit of Mauna Loa and the summit cabin (see inset on diagram). Students must interpret the graph to answer the following questions.

Click here for the handout for Activity 14.

  1. From 1966 to 1985 did the distance between the two stations increase, decrease, or remain the same? (circle one)
    The distance increased by 1.5 m.

  2. From 1966 to 1974, did the distance between the two stations increase, decrease, or remain the same? (circle one)
    The distance remained the same.

  3. What caused the rapid increase in distance in 1975 and 1984?
    Magma injection prior to and during eruptions caused the rapid increases in distance in 1975 and 1984.

  4. From late 1975 to early 1984, did the distance between the two stations increase, decrease, or remain the same? (circle one)
    The distance between the two stations gradually increased.

  5. After the onset of the eruption in March 1984, did the distance between the two stations increase, decrease, or remain the same? (circle one) What caused this change?
    The distance decreased by 20 cm. The decrease in distance was caused by the deflation of the summit as the eruption started.

Other Activities To VolcanoWorld