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Rainbows on the ground: How satellite radar helps scientists monitor volcano deformation

November 22, 2015 - 1:30am

The surface of Kilauea volcano is rarely stationary. There are a variety of processes that each move or change the shape of the volcano and, when active at the same time, create a complex pattern of ground deformation. Satellite-based Interferometric Synthetic Aperture Radar (InSAR) has become a key tool during the last two decades to illuminate this complexity.

For example, InSAR recently proved important in understanding the various episodes of Kilauea’s south caldera intrusion this past spring. In April, the shallow reservoir beneath Kilauea Caldera began to rapidly inflate, causing the lava lake within the Overlook crater to rise to the point where it overtopped its rim and spilled onto the floor of Halemaumau. It was during this time that scores of visitors crowded into the viewing area at the Jagger Museum to catch the spectacular display of spattering.

On May 11, tiltmeters began recording rapid deflation, the lava lake level dropped and earthquakes in the south caldera increased in rate and magnitude. Within a day, inflation in the south caldera was clear from our network of continuous GPS instruments and tiltmeters.

InSAR images spanning the beginning of this event show the uplift associated with the initial inflation in great detail, revealing a complexity to the shape of the reservoir that we previously only suspected. The images also capture the transition to deflation at Halemamau and south caldera inflation.

As shown in the accompanying image, the rainbow pattern seen in the interferogram beautifully captured the shape and extent of ground uplift during this event. This image shows that the uplift coincides with the location of a known south caldera storage reservoir. This is the first evidence that we have ever had suggesting rapid magma transfer between storage reservoirs.

So where do these rainbow patterns come from? The rainbow colors represent the change in distance between the ground and the satellite in the time between two orbits of the InSAR satellite. Each cycle of colors, from magenta to blue (analagous to the red to purple progression in a rainbow in the sky), indicates motion equal to half the satellite’s radar’s wavelength, or about six-tenths inch for the interferogram in the figure. The pattern repeats and by counting up all the rainbows, called “fringes,” you get the total amount of motion.

Over the past two decades, the increasing number of available satellites has improved our InSAR capabilities by providing a variety of wavelengths that allow for improved resolution at short wavelengths and better penetration through vegetation at longer wavelengths. HVO has used data from many different InSAR satellites to investigate motion on Hawaii’s volcanoes, including satellites launched by the European Space Agency, Canada, Germany and Japan.

The United States is working toward launching its first InSAR satellite. In 2014, NASA announced a joint project with the Indian Space Research Organization to build and launch a multi-wavelength InSAR satellite, dubbed the NISAR satellite, specifically designed for studying natural hazards. The ground-breaking project is scheduled for a 2020 launch. This and other upcoming satellites promise to provide even better and more frequent views of Kilauea and Mauna Loa’s deformation field and we expect even more new insights to come.

Volcano activity updates

Kilauea continues to erupt at its summit and East Rift Zone. The summit lava lake level varied between 180 and 260 feet below the vent rim within Halemaumau Crater. On the East Rift Zone, scattered lava flow activity remained within about four miles Puu Oo.

Mauna Loa is not erupting. Small earthquakes continue to occur beneath the volcano’s summit and upper Southwest Rift Zone at rates slightly above background levels. GPS lines across the summit have shown no change, but flank crossing lines continue to extend, which is consistent with inflation of magma reservoirs beneath Mauna Loa.

One earthquake was reported felt on Hawaii Island this past week. On Monday at 04:12 a.m., a magnitude-2.8 earthquake occurred two-and-one-tenth miles south of Kawaihae at a depth of 19.7 miles.

Info: hvo.wr.usgs.gov, 967-8862 for Kilauea update, askHVO@usgs.gov.

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

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