Volcano Watch — New satellite data will help to monitor deformation of Hawaiian volcanoes

The InSAR technique compares two radar images acquired by a satellite at different times to measure changes of the Earth's surface. HVO has used InSAR to measure inflation and deflation of Hawai‘i's volcanoes, ground motion caused by earthquakes, and large-scale changes in topography related to construction of new eruptive vents and accumulation of lava flows.

InSAR works best on barren, unvegetated surfaces, like recent lava flows, and requires no ground equipment. The method is therefore an excellent means of tracking surface changes at volcanoes and has resulted in many new discoveries at Kīlauea and Mauna Loa.

Since 2003, HVO has relied on the ENVISAT satellite, operated by the European Space Agency, for InSAR data. ENVISAT, however, is running low on the compound hydrazine—the fuel used to maintain the satellite's position in space. On October 22 of this year, the orbit of ENVISAT will be adjusted to conserve the valuable fuel and extend the satellite's lifetime through 2013. An unfortunate consequence of the orbit adjustment is that InSAR measurements will no longer be dependable.

To ensure that HVO maintains a reliable InSAR capability into the future, a new source of satellite radar data is needed. Such data are now available from the TerraSAR-X satellite, which was launched by the German Space Agency and has been operational since 2008.

Although similar in concept to ENVISAT, TerraSAR-X offers several noteworthy advantages. First and foremost is higher ground resolution. ENVISAT has a resolution of about 30 m (100 feet), which means that the satellite cannot "see" any features smaller than that size. In contrast, TerraSAR-X can achieve a resolution of 1 m (3 feet).

The increased resolution of TerraSAR-X, compared to that of ENVISAT, means that HVO will be able to map surface deformation on a much smaller scale than was previously possible. For example, the Pu‘u ‘Ō‘ō eruptive vent on Kīlauea's east rift zone has a crater that is approximately 400 m (1,300 feet) long by 300 m (980 feet) wide. The shape of the crater—much less any deformation that might be occurring within or around the crater—cannot be distinguished in ENVISAT data. In contrast, Pu‘u ‘Ō‘ō's features are clearly defined in images acquired by TerraSAR-X. The same is true of Kīlauea's summit eruptive vent, which is contained within Halema‘uma‘u Crater and is only 130 m (425 feet) in diameter.

Another advantage of TerraSAR-X is the frequency of image acquisition. With ENVISAT, images are acquired every 35 days, meaning that changes on Earth's surface must be cumulative over several weeks in order to be detected. In contrast, TerraSAR-X acquires data over Hawai‘i every 11 days—three times more frequently than ENVISAT!

To help develop the new data as a monitoring tool for Hawaiian volcanoes, HVO has the help of Nicole Richter, a graduate student from the University of Jena in Germany, who is an expert in TerraSAR-X data. Nicole arrived in Hawai‘i in early September and will spend 6 months at HVO processing and analyzing TerraSAR-X InSAR results as part of her thesis research. Her primary goal is to use InSAR data from TerraSAR-X to map surface deformation at Kīlauea and Mauna Loa over time, focusing on inflation and deflation of Kīlauea's summit and east rift zone eruptive vents.

Nicole will also explore the use of data from TerraSAR-X to create topographic maps of Kīlauea's surface to record large-scale changes in volcanic activity. For example, HVO can use topographic maps created from TerraSAR-X data to monitor collapses of the Halema‘uma‘u or Pu‘u ‘Ō‘ō eruptive vents. Similarly, by comparing how the topography of Kīlauea's lava flow field changes over time, we can determine the volume of lava that is accumulating on the surface and provide a measurement of the lava eruption rate.

The improved capabilities of TerraSAR-X will result in a new perspective of surface change at Hawaiian volcanoes. HVO is pleased with the partnership that has developed with the German Space Agency, which will ensure a continuing stream of high-quality satellite data in support of our volcano and earthquake monitoring and research efforts.

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

Volcano Activity Update

No active surface flows from Kīlauea's east rift zone eruption have been observed over the past week. Small flows were active within the Pu‘u ‘Ō‘ō crater last weekend, but no incandescence has been seen via Webcam since. Lava continues to enter the lava tube system, however, and is carried downslope to Puhi-o-Kalaikini, near Kalapana, where it enters the ocean. The vigor of the ocean entry steam plume has waxed and waned over the past several weeks, recording fluctuations in the amount of lava being erupted. These fluctuations are caused by the frequent deflation-inflation cycles impacting the volcano.

At Kīlauea's summit, the circulating lava lake deep in the collapse pit within the floor of Halema‘uma‘u Crater has been visible via Webcam throughout the past week. The lava level has fluctuated slowly in tandem with the deflation-inflation cycles. This slow change has also been interrupted sporadically by abrupt increases in the height of the lava surface. These periods of high lava level have been short-lived, lasting up to several hours, and each ended with a sudden drop of the lava surface back to its previous level. Volcanic gas emissions remain elevated, resulting in high concentrations of sulfur dioxide downwind.

One earthquake beneath Hawai‘i Island was reported felt during the past week. A magnitude-2.9 earthquake occurred on Wednesday, September 22, 2010, at 1:03 p.m. H.s.t., and was located 2 km (1 mile) northeast of Hōlualoa at a depth of 36 km (22 miles).