Volcano Watch: DI events at Kilauea – what are they and what do they mean?

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This movie is from images captured by a camera positioned on the north rim of Pu‘u ‘O‘o, looking into the crater from March 23–29, 2012. Dimensions of crater are approximately 400 m long (left to right in webcam) and 250 m wide (straight ahead).

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

Tilt measured at the summit of Kilauea during March 1–€“7, 2012, shows a series of U- and V-shaped DI events, with deflation indicated by downward tilt and inflation by upward tilt.  Images from a thermal camera that overlooks the summit eruptive vent demonstrate how the lava level (noted by white dashed line), depicted by warmer colors, charges across tilt cycles. Tilt is measured in microradians, with one microradian equivalent to the change in slope caused by putting a dime under one end of a bar that is 1 km (2/3 mile) long.

Tilt measured at the summit of Kilauea during March 1–€“7, 2012, shows a series of U- and V-shaped DI events, with deflation indicated by downward tilt and inflation by upward tilt.  Images from a thermal camera that overlooks the summit eruptive vent demonstrate how the lava level (noted by white dashed line), depicted by warmer colors, charges across tilt cycles. Tilt is measured in microradians, with one microradian equivalent to the change in slope caused by putting a dime under one end of a bar that is 1 km (2/3 mile) long.

As alert volcano watchers are no doubt aware, recent activity at Kilauea has been to “DI” for. Repeated deflation-inflation, or DI, events are currently dominating deformation of the volcano and have been a familiar theme in daily activity updates since 2008. But what are DI events, and what do they mean?

DI events are characterized by sudden deflation that lasts for 1–3 days, followed by equally sudden inflation that returns the tilt to pre-event levels. This gives the tilt events a V- or U-shaped appearance in tilt records (see for yourself in the tilt data at hvo.wr.usgs.gov/kilauea/update…). The total amount of subsidence during deflation and subsequent uplift during inflation is usually only about an inch (2.5 cm) and appears to be caused by pressure changes about 1 km beneath the east margin of Halema`uma`u Crater.

The tilt events are not only recorded at Kilauea’s summit, but also at Pu`u `O`o. Tilt at the east rift zone eruption site has the same overall form as that at the summit but lags behind by a few hours as the pressure change propagates from the summit to Pu`u `O`o.

DI events are often associated with changes in eruptive activity. During the deflation phase, lava effusion at Pu`u `O`o tends to decrease and the summit lava column lowers, while the inflation phase is accompanied by a rise in the summit lava column and sometimes a surge in lava from Pu`u `O`o.

USGS geochemist Michael Poland explains how a tilt-meter works. The device contains a liquid level and is placed in the ground near the summit of a volcanic site. The device will lean away from the vent when the summit is inflating and towards the vent during deflation. Many of the remote sensing devices use WiFi to broadcast data. Hawaii 24/7 File Photo.

The start of Kilauea’s summit eruption in 2008 caused a major change in the style of DI events. Prior to 2008, the number of tilt events averaged 5–10 per year. In 2008, however, there were 47 events. In 2009, 2010, and 2011, there were 64, 68, and 87 events, respectively. Thus far in 2012, there have been 37 events, on pace to shatter the records from previous years.

The 2008 increase in numbers of DI events corresponds to the start of the summit eruption, when gas emissions from the summit increased markedly (by about a factor of 4–5). As magma loses gas, it becomes denser and sinks, allowing less dense, gas-rich magma to rise towards the surface. This convection, similar to what can be seen in a boiling pot of soup, is common in magma chambers and can even be observed from circulation patterns within Kilauea’s summit eruptive vent. DI events might be an expression of such convection, with the deflation phase corresponding to sinking of dense magma, and inflation resulting from the rise of gas-rich magma.

While satisfying in its simplicity, this model for DI events cannot explain all aspects of their occurrence. For example, there were no DI events during the last two months of 2010, but the first three months of 2011 saw almost continuous DI cycles. Similarly, DI events have been occurring one after the other since the start of 2012. Through it all, gas emissions have remained relatively steady, even decreasing slightly from their 2008 peak. More study is clearly necessary to test ideas about the possible cause of DI events.

Nevertheless, DI events, while minor in terms of their overall magnitude of deformation, are important to Kilauea’s eruptive activity. Frequent DI events can disrupt lava flows from the east rift zone, while periods of no DI events can allow lava from Pu`u `O`o to develop robust tube systems to the ocean. Continued monitoring of ground tilt, gas emissions, and other data will undoubtedly reveal even more about these enigmatic events.

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