Interpreting Ground Displacement I (Grades 9-12)
In 1971, the feeder conduit to the
eruption site became
blocked. Magma continued to be supplied to the summit reservoir from the
mantle and caused rapid summit inflation. Pressure reopened the conduit
in February 1972, and the eruption continued. The period of rapid summit
inflation was interrupted by two eruptions in 1971. On August 14, a
10-hour-long eruption occurred in Kilauea Caldera. On September 24, an
eruption began in the caldera and, by the 29th, migrated 12 km down the
southwest rift zone. Prior to the eruption in September, uplift occurred
along the upper southwest rift zone. The pattern of uplift is shown in
activity 12.8. The uplifted area is elongate and centered along the rift
zone (Duffield and others, 1982).
here to see Activity 8.
Students must study the diagram to answer the following questions.
- Is the center of ground displacement at Halemaumau Crater, the
east rift zone, or the upper southwest rift zone? (circle one)
The ground displacement is centered on the upper southwest rift zone.
- Does the ground displacement pattern indicate uplift or
The ground displacement contours along the
rift zone are positive, indicating uplift. The tilt vectors also point
radially outward, a pattern common for uplift. The single -2.5 mm
contour for a small area northeast of the caldera indicates subsidence.
- What is the maximum amount of ground displacement?
Maximum uplift is greater than 45 mm but less than 50 mm.
- What type of volcanic activity would you expect to be associated
this ground displacement pattern?
The relatively large
amounts of uplift
indicate the intrusion of magma into the upper southwest rift zone and
the potential for a fissure eruption. An eruption did occur along the
axis of the uplift.
- Where is volcanic activity likely to occur?
eruption would be along the southwest rift zone.
- Why are the lines dashed for the southwest part of the
No data was obtained for that area because it is rugged and difficult to
- Are the tilt vectors useful for defining the center of ground
Yes. Most of the vectors project to the
center of the
uplift. The two southwesternmost tilt vectors were influenced by the
central uplift and the elongated uplift along the rift.