Volcano Watch — Surface Deformation at Kīlauea's Summit is a Moving Target

As magma moves beneath the Earth's surface, the ground deforms to accommodate the changing volume below. For example, when magma accumulates in a subsurface chamber, the ground inflates like a giant balloon. But when magma drains from a chamber and erupts, for example, on Kīlauea's east rift zone, the surface deflates. The extent of this deformation is usually small (perhaps tens of centimeters/inches each year), but in extreme cases at some volcanoes, it can be more than several meters (over 10 feet)!

HVO monitors these changes using a variety of methods. (1) To map motion of the surface over a broad region, we utilize radar data collected by orbiting satellites. (2) To track surface motion continuously in three dimensions at several places around Kīlauea, we employ GPS stations. (3) To measure tilt of the Earth's surface, we use tiltmeters installed in shallow boreholes. (4) To measure changes in elevation that are accurate to a fraction of a millimeter, we conduct leveling surveys around Kīlauea once a year. While the first three techniques listed are relatively new, leveling has been done at Kīlauea, using the same basic technology, since 1912.

These measurements reveal how ground motion is related to magma movement beneath the surface at Kīlauea. During much of the Pu`u O`o-Kupaianaha eruption, Kīlauea's summit deflated, with the maximum deformation located about 2 km (1 mile) south of Halema`uma`u Crater. Compared to its 1983 elevation (at the start of the Pu`u `O`o eruption), the southern part of the caldera had subsided by about 1.5 m (over 4 feet) by 2003!

Since 2003, however, an influx of new magma to Kīlauea has caused a truly astonishing migration of the deformation source over time.

During 2003-2004, inflation was centered along the east wall of Halema`uma`u Crater, not far from the currently active summit vent. One year later, inflation was centered closer to Keanakako`i Crater, in the southeast part of the caldera. During 2005-2006, the focal point of inflation was the south caldera-the same source that had been deflating from 1983 to 2003.

Alert volcano watchers will know that activity at Kīlauea changed abruptly in June 2007, when an intrusion and eruption occurred between the summit and the east rift eruptive vent at Pu`u `O`o, followed one month later by the opening of a new eruptive vent 2 km (1 mile) east of the crater. This new vent has been the main source of erupting lava to this day, and is the source of the lava flows that can be seen entering the ocean near Kalapana. Since then, Kīlauea's summit has been deflating, probably because more lava is erupting from the new vent than is being supplied to the volcano.

Like the 2003-2007 pattern of inflation, the recent deflation has been moving around the summit area like a caged tiger. At first, the deflation was focused on the east rim of Halema`uma`u Crater—but by late 2007 had moved to the south caldera. In mid-2008 (after the start of the summit eruption), the center of deflation had moved back to Halema`uma`u's east rim-but by late summer had returned to the south caldera.

What does this strange dance mean? Why would the center of deformation at Kīlauea move in apparently erratic ways? This is not the first time such behavior has been observed at Kīlauea.

Before the 1967-1968 summit eruption (which was the subject of last week's column), leveling measurements by HVO showed a highly variable center of inflation. During 1966-1967, the source of uplift moved from east of Halema`uma`u to the south caldera, then to the southwest caldera, and finally back to the south caldera-all prior to the eruption.

All these changes at Kīlauea's summit reveal the complexity of the magma storage areas beneath us. Although we often think of a magma chamber as a giant balloon, the actual geometry of the magma reservoir is probably much more complicated, with several interconnected storage areas. The moving deformation source suggests that different parts of Kīlauea's magma system are active at different times.

Unusual eruptive activity characterized the migrations of the deformation source during both 1966-1967 and 2003-present eruptions. Perhaps this deformation behavior indicates that Kīlauea is especially active, and that large volumes of magma are moving underground. Certainly the fist summit eruption in more than 25 years is an indication of Kīlauea's restless state. With the latest in deformation-monitoring technology, HVO is well-positioned to track Kīlauea's ever-changing shape and learn even more about how magma is stored within the house of Pele.

————————————————————————————————————————————————————————————————

Volcano Activity Update

Kīlauea Volcano continues to be active. A vent in Halema`uma`u Crater is erupting elevated amounts of sulfur dioxide gas and very small amounts of ash. Resulting high concentrations of sulfur dioxide in downwind air have closed the south part of Kīlauea caldera and produced occasional air quality alerts in more distant areas, such as Pahala and communities adjacent to Hawai`i Volcanoes National Park, during kona wind periods. The have been several small ash-emission events from the vent, lasting only minutes, in the last week.

Pu`u `Ō`ō continues to produce sulfur dioxide at even higher rates than the vent in Halema`uma`u Crater. Trade winds tend to pool these emissions along the West Hawai`i coast, while Kona winds blow these emissions into communities to the north, such as Mountain View, Volcano, and Hilo.

Lava continues to erupt from the Thanksgiving Eve Breakout (TEB) vent and flows toward the ocean through a well-established lava tube. Lava breakouts in the Royal Gardens subdivision have been active throughout the past week, sending small flows several hundred yards southward onto the coastal plain. Activity at the Waikupanaha ocean entry has fluctuated over the past week. A deflation-inflation (DI) event at the summit led to a brief reduction in activity at the ocean entry on Wednesday, November 12.

Be aware that active lava deltas can collapse at any time, potentially generating large explosions. This may be especially true during times of rapidly changing lava supply conditions. Do not venture onto the lava deltas. Even the intervening beaches are susceptible to large waves generated during delta collapse; avoid these beaches. In addition, steam plumes rising from ocean entries are highly acidic and laced with glass particles. Check Civil Defense Web site or call 961-8093 for viewing hours.

Mauna Loa is not erupting. One earthquake was located beneath the summit this past week. Continuing extension between locations spanning the summit indicates slow inflation of the volcano.

One earthquake beneath Hawai`i Island was reported felt within the past week. A magnitude-2.7 earthquake occurred at 10:52 a.m., H.s.t., on Friday, November 7, 2008, and was located 12 km (7 miles) southwest of Kīlauea summit at a depth of 30 km ( 19 miles).

Visit our Web site for daily Kīlauea eruption updates, a summary of volcanic events over the past year, and nearly real-time Hawai`i earthquake information. Kīlauea daily update summaries are also available by phone at (808) 967-8862. Questions can be emailed to askHVO@usgs.gov. skip past bottom navigational bar