Tilt, Eruptions, and Earthquakes (Grades 9-12)

The relationships between tilt, eruptions, and earthquakes are explored, using the graphs in activity 10. These data are from the ongoing eruption of Kilauea Volcano when activity was characterized by high lava fountains at the Puu Oo vent (Wolfe and others, 1987).

Students are required to interpret the graph to answer the following questions.

1. Is there a correlation between tilt and eruptions?
Yes. Each eruption is marked by rapid subsidence of the summit.

2. In terms of tilt, what happens at the summit before eruptions?
The summit of the volcano gradually inflates between eruptions.

3. Does the summit inflate to the same tilt angle prior to each eruption?
No. For example, compare episode 15 and 17.

4. Do short-period caldera earthquakes correlate with tilt and/or the eruptive episodes?
Yes. During the eruptive episodes, the number of short-period caldera earthquakes is low. As the summit inflates after each eruption, the number of short-period caldera earthquakes gradually increases.

5. Do long-period caldera earthquakes correlate with tilt and/or the eruptive episodes?
Yes. Large numbers of long-period caldera earthquakes occur during rapid summit deflation and eruptive episodes. Long-period caldera earthquakes are rare between eruptive episodes.

6. Does summit tremor correlate with tilt and/or the eruptive episodes?
Yes. Summit tremor increases during rapid summit deflation and eruptive episodes. Summit tremor is rare between eruptive episodes.

7. Based on the data presented in the graphs, outline the geologic events leading up to, during, and after an eruptive episode.
• Magma accumulates in the summit reservoir, causing the volcano to inflate and tilt to increase.

• As more magma accumulates and the volcano continues to inflate, the rocks above and around the magma reservoir deform and create short-period caldera earthquakes.

• At the onset of the eruptive episode, magma leaves the summit reservoir causing the summit to rapidly deflate. Summit tremor indicates that the magma is moving. Long-period caldera earthquakes indicate that magma is rising from deep beneath the volcano to resupply the summit reservoir.

• After the eruption, the cycle, with some minor variations, is repeated.
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