## Interpreting Tilt Vectors (Grades 9-12)

Prior to the onset of the current eruption of Kilauea Volcano, the summit of the volcano inflated. The pattern defined by the tilt vectors is shown in activity 9. Figure A shows a radial pattern, with the vectors pointing away from an area south of Halemaumau Crater. This pattern reflects uplift of the summit from August 12-14, 1981, to March 3-April 5, 1982 (Dvorak and Okamura, 1987). Figure B also shows a radial pattern, but the vectors point towards the area south of Halemaumau Crater. This pattern reflects the subsidence of the summit from September 27-October 14, 1982, to February 2-11, 1983.

Students must interpret the patterns defined by the tilt vectors to answer the following questions.

1. Do the tilt vectors in figure A indicate inflation or deflation of the summit?
The tilt vectors point radially outward from the summit, suggesting inflation.

2. Is the maximum amount of tilt in the caldera, around the edge of the caldera, or far from the caldera? (circle one)
The maximum amount of tilt is around the edge of the caldera.

3. Use a ruler to draw lines in the direction opposite to the tilt vector. Repeat for 5 to 10 stations (shown by triangles). The intersection of the lines should define a small area. What is the significance of this area?
The lines intersect at the center of the uplift.

4. Does the area defined in Question 3 correspond with Halemaumau Crater? How far and in what direction is the area from Halemaumau Crater?
The center of the uplift is 1.5 km south of the crater.

5. Why is the area defined in Question 3 not located at Halemaumau Crater?
The area defined in Question 3 probably marks the top of the magma reservoir beneath the summit. Its location may indicate that the reservoir is migrating to the south with time.

6. Do the tilt vectors in figure B indicate inflation or deflation of the summit? (circle one)
The tilt vectors point radially inward toward the summit, suggesting deflation.

7. Does the area of maximum uplift correspond with the area of maximum deflation?
Yes. The area of maximum uplift corresponds with the area of maximum deflation.
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