Volcano Watch — HVO intern increases understanding of deformation at Kīlauea Volcano

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Ben's work on explosive deposits at Kīlauea's summit was an important step in understanding the causes and consequences of explosive eruptions in Hawai`i.

Sarah Menassian, another student in the course, also did her internship at HVO, focusing on the timing and patterns of deformation at Kīlauea Volcano.

HVO uses a variety of techniques to determine how the ground's surface deforms over time. The data can then be used to locate magma in the subsurface, which is important when forecasting future volcanic activity.

The methods currently in use by HVO include Global Positioning System (GPS), tilt, and leveling (elevation change) measurements. HVO maintains a network of over 40 continuous GPS stations, which chart ground motion in three dimensions on a daily basis. Similarly, a network of 18 tiltmeters detects subtle changes in the slope or tilt of the Earth's surface. Leveling surveys, conducted 1-2 times per year, can identify changes in vertical elevation with millimeter-level precision.

Since the Pu`u `O`o eruption began in 1983, Kīlauea's caldera has been subsiding, with the area south of Halema`uma`u Crater sinking by about 1.5 meters (5 feet) between 1983 and 2002. After 2002, a small area immediately northeast of Halema`uma`u started to rise.

Leveling surveys in 2005 showed still another curious change. Although uplift continued near Halema`uma`u, a greater amount of uplift was occurring near Keanakako`i Crater. The annual leveling surveys, unfortunately, could not tell precisely when this new uplift began, and the data from continuous GPS and tilt sites were too sparse to detect this change.

Data from radar interferometry (InSAR) might be useful in determining when the uplift near Keakakako`i began. InSAR uses radar images acquired by a satellite at two different times to detect deformation changes of the Earth's surface. The advantage of InSAR over other techniques is that ground deformation information from almost anywhere that is not thickly vegetated, including Kīlauea's caldera and rift zones, can be recovered. But these results are available only about once per month, when the satellite collects an image.

As part of her internship at HVO, Sarah worked on writing a program that would ingest a large amount of InSAR data and calculate the average deformation over time at approximately monthly intervals. By analyzing several dozen InSAR images collected between 2003 and 2006, Sarah was able to shed light on a number of different processes.

First, Sarah looked at deformation in Kīlauea's two rift zones. She found that both were subsiding at constant rates of 1-2 centimeters (0.4-0.8 inches) per year. Next, she focused on Kīlauea's summit and found that the north part of the caldera was subsiding at constant rate of about 1 centimeter (0.4 inches) per year, while the area northeast of Halema`uma`u was uplifting at a rate of about 2 centimeters (0.8 inches) per year.

The most surprising result came from the Keanakako`i area. Sarah's results showed that before May 2004, no significant ground motion occurred in that region of the caldera. From May 2004 to January 2006, however, uplift occurred at a rate of over 4.5 centimeters (1.75 inches) per year - much higher than deformation rates anywhere else in the summit region! Thus, Sarah's data confirm that uplift in the Keanakako`i area is relatively recent, from the leveling results, and further suggest that the uplift began in early summer, 2004.

The programs that Sarah wrote during her time at HVO can also be applied to other locations where InSAR is used to measure ground deformation, including Mauna Loa Volcano, which has been inflating since 2002.

Sarah's work was an important step in understanding the recent changes that have taken place at Kīlauea. She made a valuable contribution during her stay, and left HVO with a tool that we will be able to use far into the future. Thank you, Sarah, and good luck in completing your studies at Cornell!

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Volcano Activity Update

This past week, activity levels at the summit of Kīlauea Volcano have remained at background levels. The number of earthquakes located in the summit area is low (usually less than 10 per day). Widening of the summit caldera, indicating inflation, appears to have resumed after pausing earlier in April.

Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from several vents within the crater. Lava continues to flow through the PKK lava tube from its source on the flank of Pu`u `O`o to the ocean, with frequent surface flows breaking out of the tube near the 2,300-ft elevation, and a persistent flow, known as the "March 1 breakout," active on the coastal plain. The March 1 breakout is waning, however, and active lava was limited to a small area 1.8 km (1.1 miles) from the coast.

Lava continues to enter the ocean at East Lae`apuki, in Hawai`i Volcanoes National Park. The active lava bench continues to grow following the major collapse of November 28 and is now approximately 1,000 m (3,300 ft) long by 315 m (1,000 ft) wide, with a total surface area of 17 ha (43 acres).

Access to the ocean entries and the surrounding area remains closed, due to significant hazards. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

There were two earthquakes beneath Hawai`i Island reported felt within the past week. A magnitude-2.1 earthquake occurred at 9:55 p.m. H.s.t. on Sunday, May 21, and was located 8 km (5 miles) northeast of Waiki`i at a depth of 16 km (10 mile). A magnitude-2.8 earthquake occurred at 5:27 p.m. H.s.t. on Monday, May 22, and was located 5 km (3 miles) south of Volcano at a depth of 4 km (2 miles).

Mauna Loa is not erupting. During the past week, earthquake activity remained low beneath the volcano's summit (no earthquakes were located). Extension of lengths between locations spanning the summit, indicating inflation, continues at slow rates.