There's something in the way a volcano moves

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Over the past four weeks, we have discussed how scientists monitor volcanoes using geophysics, geology, gas geochemistry, and seismology. As we reach the end of January and the second annual Volcano Awareness Month, we conclude our discussion of volcano monitoring by exploring deformation measurements.

There's something in the way a volcano moves...

An HVO scientist wearing a gas mask collects GPS data using a roving instrument on the west flank of Pu‘u ‘Ō‘ō. USGS Photo.

(Public domain.)

As magma accumulates in subsurface reservoirs, it makes space for itself by expanding the reservoir walls. This motion causes the surface above the reservoir to rise. Likewise, when magma drains from a reservoir beneath the ground, the surface subsides. The pattern of surface deformation caused by magma accumulation and withdrawal is similar to that of a balloon being inflated and deflated.

By measuring surface deformation—inflation and deflation—volcanologists can assess the volume of magma that is accumulating or draining and can also estimate the depth of the magma reservoir. Any changes in the deformation pattern of a volcano indicate that magma is moving beneath the surface and can aid in assessing the likelihood of eruption.

Surface displacements at volcanoes tend to be small by human standards. Typical changes might amount to only a few centimeters or millimeters (inches or fractions of an inch). Yet over the broad distances spanned by Kīlauea and Mauna Loa, these small displacements reflect large amounts of magma beneath the surface. But how is it possible to measure surface deformation with such precision?

The current workhorse of volcano deformation monitoring is something that is familiar to most people—the Global Positioning System (GPS). HVO uses very sensitive GPS receivers, different from those you might use in your car or while hiking, to measure positions to within a few millimeters (fractions of an inch). GPS provides both vertical and horizontal deformation and has been instrumental in mapping the locations of, and volume changes within, subsurface magma reservoirs at Kīlauea and Mauna Loa over the last 20 years.

By installing a permanent GPS station in one location and running it continuously, changes in that position can be tracked over time. HVO collects data from over 60 continuous GPS stations on the Island of Hawai‘i. In addition, annual or biannual GPS surveys are carried out to supplement the continuous data, and mobile GPS rovers are used in highly active places, such as the Pu‘u ‘Ō‘ō eruptive vent, to measure localized ground displacements.

HVO also has 20 continuously operating tiltmeters on Kīlauea and Mauna Loa. Tiltmeters, which are instruments that measure very small changes in the slope of the Earth's surface over time, are installed in boreholes, about 2-3 m (6-9 feet) beneath the surface. Borehole installations insulate the tiltmeters against surface noise caused by temperature changes and other environmental effects. Alert readers who follow Kīlauea's daily eruption update may have noticed that Kīlauea experiences cycles of deflation and inflation—so-called "DI events"—every few days or weeks. These events were first detected and are best measured using tiltmeters.

In addition to ground-based instruments, HVO scientists also utilize space-based sensors to measure ground deformation. Interferometric synthetic aperture radar, or InSAR, measurements use radar images of the surface acquired at different times to calculate changes in the distance between the satellite and the ground between the times that the images were taken.

As we conclude our month-long look at volcano monitoring, it is important to remember that no single monitoring type is the "magic bullet" that answers all questions about volcanic activity. Geophysics, geology, gas geochemistry, seismology, and deformation must be used in combination to best assess the level of volcanic activity and the potential for future eruption. The HVO staff includes experts in all these fields, making the Observatory a one-stop shop for volcano monitoring!

We hope you have enjoyed this series of articles on how HVO scientists monitor the volcanoes of Hawai‘i, as well as other events associated with Volcano Awareness Month. The final talk of the month, about the history and current status of Mauna Loa, will be at the Lyman Museum on January 31.

Best wishes for happy and safe 2011 from the staff of the Hawaiian Volcano Observatory!


Volcano Activity Update

Over the past week, lava flows have been active on the pali and coastal plain in two distinct lobes west of Kalapana. The easternmost of the active flow lobes continues to advance slowly to the south and southeast near the end of Highway 130, one portion creating a small ocean entry. The western lobe has scattered breakouts throughout its length on the coastal plain.

At Kīlauea's summit, the circulating lava lake in the collapse pit deep within the floor of Halema‘uma‘u Crater has been visible via Webcam throughout the past week. Several pieces of the Halema‘uma‘u crater floor collapsed into the lava lake at 2:30 and 2:38 p.m. on January 21. The largest collapse caused a small explosion that littered the rim of Halema‘uma‘u crater downwind of the vent with spatter up to 8 cm (3 in) across. The opening on the floor of Halema‘uma‘u crater is now 144 m (472 ft) east-to-west by 142 m (466 ft). The circulation pattern of the lava lake was interrupted by the explosion, and only a few short-lived increases in the height of the lava surface have occurred since Tuesday, January 25. A DI event spanning several days occurred this week but has leveled off since Monday afternoon (January 24). Volcanic gas emissions remain elevated, resulting in high concentrations of sulfur dioxide downwind.

Three earthquakes beneath the Hawaiian Islands were reported felt Wednesday night and Thursday morning. A magnitude-2.4 earthquake occurred at 8:45 p.m. (HST) on Wednesday, January 26, 2011, and was located 2 km (1 mile) northeast of Kīlauea summit at a depth of 2 km (1 mile). A magnitude-1.8 earthquake occurred at 9:25 p.m. later that same night, and was located 3 km (2 miles) northeast of Kīlauea summit at a depth of 1 km (1 mile). A magnitude-1.9 earthquake occurred at 7:51 a.m. on Thursday, January 27, and was located 4 km (3 miles) southwest of Pu‘ulena Crater at a depth of 0 km (0 miles).