Tiltmeters track inflation and deflation of Kilauea's summit caldera

Lava fountain at Pu`u `O`o vent, Kilauea Volcano, Hawai`i

Photograph by J.D. Griggs
on 4 February 1985

Spectacular eruptions of Pu`u `O`o on the east rift zone of Kilauea Volcano between 1983 and 1986 were accompanied by a remarkable pattern of ground tilt at the volcano's summit about 20 km away. Before erupting at Pu`u `O`o, magma first moved into the underground summit reservoir beneath the summit caldera then into the volcano's east rift zone. As the magma moved from the summit reservoir toward Pu`u `O`o, the ground at the summit subsided, which was recorded by tiltmeters on the west rim of the caldera.

Magma inflates and deflates Kilauea Volcano

Kilauea caldera, Hawai`i

Kilauea's summit caldera
Photograph by D. Dzurisin on 12 September 1980

View northeast across Kilauea caldera. Halema`uma`u Crater in low center is 1 km in diameter. The USGS Hawaiian Volcano Observatory is located on the west rim of the caldera (small group of buildings near road, center left).

More than 40 years of tiltmeter records show that magma moving beneath the summit caldera of Kilauea Volcano forces the ground to move up and down, sometimes by as much as 2 m. When magma pushes the summit caldera up, tiltmeters located on the caldera rim tilt outward. The longest record of tilt at Kilauea is from a tiltmeter in the Uwekahuna vault located near Hawaiian Volcano Observatory.

Kilauea caldera, Hawai`i

Tilt of Kilauea's summit caldera

This graph shows a one-year record of tilt from the Uwekahuna tiltmeter located on rim of Kilauea's caldera. When the tiltmeter record showed an increase in slope angle (microradians) the ground was tilting away from the caldera, which indicates the summit area was inflating with magma. Then, when lava within Pu`u `O`o filled and overflowed the crater or began fountaining, the summit tiltmeter record suddenly showed a decrease in slope angle or deflation. After the eruption, the tiltmeter once again recorded a steady outward tilt. What can we learn by this change in pattern of ground tilt at the summit and eruptive activity at Pu`u `O`o 20 km away?

Sketch showing magma pathways beneath volcano

Magma pathways beneath Kilauea Volcano

Magma rising into Kilauea Volcano first enters a principal storage reservoir beneath its summit caldera. The magma may then erupt at the summit or move through one of two principle pathways (rift zones) beneath the flanks of Kilauea (arrows show direction). This movement of magma down the rift zones causes the summit area to subside, which is recorded by tiltmeters as an inward tilt of the caldera rim. When magma is not moving down one of the rift zones, the summit caldera inflates slowly as shown by an increase in ground tilt, indicating magma is rising into the summit reservoir.

Aerial view of Kilauea Volcano's summit caldera and east rift zone

The east rift zone of Kilauea Volcano
Photograph by J.D. Griggs on 1 January 1985

A series of craters, cinder cones, and ground fractures leading from the summit caldera of Kilauea Volcano marks the east rift zone (line shows approximate location of rift zone between caldera and Pu`u `O`o). The rift zone consists of a series of fractures within the volcano through which magma moves from the summit reservoir. Kilauea's summit caldera and Halema`uma`u crater are in foreground. A gas plume from Pu`u `O`o rises in the background.

The remarkable tilt pattern at the caldera in the 1980's showed that the summit magma reservoir is often in delicate balance with the reservoir system beneath the east rift zone. The pattern of tilt at Kilauea helps scientists determine when magma is on the move down one of the rift zones and when it might erupt.

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