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Mauna Loa is inflating again

Oblique shaded-relief map of Island of Hawai`i
Oblique shaded-relief map of the five volcanoes that built the Island of Hawai`i. Mauna Loa encompasses 51 percent of the island's surface area; its most recent eruption was in 1984. Click for large map.

Continuously recording GPS receivers were installed on the summit and upper flanks of Mauna Loa in 1999 to detect changes in shape of the volcano that typically accompany underground movement of magma. The GPS instruments allow such ground deformation to be tracked continuously and also more accurately than was possible before.

Until May of this year, the new instruments showed what we already knew from other surveying techniques—the summit caldera was slowly subsiding and shrinking.

But in late April to late May, centered on May 12 (Mother's Day), the GPS receivers began moving slightly in a different direction. Since May, the instruments show that Mauna Loa's summit area is rising slightly and the caldera is widening 5-6 cm per year.

What caused the abrupt change? Our computer models of the moving GPS receivers suggest that the current ground motion is the result of magma rising into a reservoir about 5 km below the caldera. Only time will tell if this new trend will continue in the coming months.

The nature of seismicity changed several months before each of the latest two eruptions. Large increases were obvious in both the numbers of earthquakes and the amount of energy released by these earthquakes. That is a reasonable expectation before the next eruption, though we must be cautious in saying that such an increase must occur. For more information, see:

Archive of previous feature stories

  Aerial view of Pu`u `O`o crater, Kilauea Volcano, Hawai`i
Photograph by R. Hoblitt
20 September 2002
Top: Aerial view of Pu`u `O`o crater looking southwest. Fume rises from spatter cones and other vents located on crater floor and south crater wall. Pu`u `O`o emits about 1,500 tonnes of sulfur dioxide gas a day.

Bottom: Close view of skylight above lava tube for Mother's Day flow, located on southwest flank of Pu`u `O`o. HVO scientists dubbed this the "cookie monster" skylight. Edifice around skylight was built by spatter tossed from lava in tube. This tube supplies all lava downstream in Mother's Day flow.

Archive of Featured Photographs

  Skylight named "Cookie Monster" on southwest flank of Pu`u `O`o, Kilauea Volcano
Photograph by J. Kauahikaua
27 September 2002


More Volcano Information from HVO and Beyond

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Volcano WatchCurrent issue of Volcano Watch essay, written weekly by USGS scientists.
National Park ServiceHawai`i Volcanoes National Park, home to HVO. Find visitor information and resources here. Graphic: Kids DoorVolcanoes for kids, from the Volcano World website.