This interferogram spans from 4/11/2015 to 5/22/2015 and shows a beautiful bullseye pattern of rainbow fringes due to about 10 cm (4 inches) of ground deformation during an intrusion this past spring. HVO graphic.

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

The surface of KÄ«lauea 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.

ESA’s Envisat environmental satellite. Image by ESA

For example, InSAR recently proved important in understanding the various episodes of Kīlauea’s south caldera intrusion this past spring. In April of this year, the shallow reservoir beneath Kīlauea 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 Halemaʻumaʻu. 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 Halema’ma’u 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.

Data interferometrically processed by HVO showing the interferogram for the period 11 April to 20 June of 2007 illustrating very clearly many surface movements. For example the fringes in the Kilauea Caldera area suggest a summit deflation due to magma movement.

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 1.5 cm (0.6 in) 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 Hawaiʻi’s volcanoes, including satellites launched by the European Space Agency (ESA), Canada, Germany and Japan.

Artist concept of NISAR satellite.

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