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Volcanowatch

March 18, 2010

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


Kīlauea's summit eruption turns two

The lava surface deep within the Halema`uma`u Overlook vent can sometimes only be seen using an infrared camera, as in this view from Wednesday afternoon, March 17.
The lava surface deep within the Halema`uma`u Overlook vent can sometimes only be seen using an infrared camera, as in this view from Wednesday afternoon, March 17.

This past Friday, March 19, marked the second anniversary of Kīlauea's ongoing summit eruption in Halema`uma`u Crater. After 25 years without eruptive activity at Kīlauea's summit, the current eruption surprised many when it blasted onto the scene two years ago.

The early morning vent-opening explosion that started the eruption scattered rocks up to a meter (yard) wide onto the rim of Halema`uma`u Crater. In the process, a glowing hole about 35 m (115 ft) wide was formed at the base of the southern wall of Halema`uma`u crater.

Over the following few weeks, the volcanic plume billowing from the vent carried tiny rock particles forming sandy black dunes that blanketed the ground downwind from the vent. Then, on April 9, 2008, part of the vent rim collapsed into the hole and initiated a small explosion that scattered more rocks and spatter onto the rim of Halema`uma`u.

While small collapses had been common since the vent opened, this was the first of dozens of large collapses that occurred as the vent evolved from a relatively small opening into what would eventually become a collapse crater about 130 m (427 ft) across. Each of these collapses was marked by a dusty brown plume that was distinctly different in appearance from the white, steam-rich gas plume that typically rose from the vent. Though most of the collapses were relatively benign, seven of them, including the April 9 event, initiated explosions that scattered rocks and spatter onto the rim of Halema`uma`u. These explosive eruptions all occurred within the first seven months of the eruption.

As the mouth of the vent widened, it began to chew its way into the floor of Halema`uma`u Crater. By early September 2008, the opening had grown large enough that Hawaiian Volcano Observatory (HVO) scientists were finally able to see through the more-dispersed gas plume to a spattering lava surface below. Occasional glimpses of lava continued until early December when, after nine months of near-continuous eruptive activity, a series of large collapses choked the vent with rubble from the vent rim and walls, extinguishing the glow and causing a pronounced decrease in gas levels and seismic tremor. There was discussion at the time about whether or not the eruption was over, but the debate ended when the glow, gas, and tremor returned in late January 2009.

The resumption in activity was accompanied by more collapses and more widening of the vent. This led to even better views, and the lava surface was commonly visible deep within the vent from March through June 2009. Scientists studying the vent were able to document vent processes at a level of detail never before achieved. It was during this period that accurate vent-dimension measurements finally revealed that the lava surface was nearly 200 m (656 ft) below the floor of Halema`uma`u, or 285 m (935 ft) below the crater's rim.

The eruption changed again on June 30, when another series of collapses plugged the bottom of the vent. As before, with the lava surface buried beneath rubble, the glow disappeared, and the gas emissions and seismic tremor both decreased dramatically. As before, however, the debris choking the vent was slowly consumed by the lava below, and the eruption resumed in mid-August.

The second half of 2009 was much the same as the first half. At times, a ponded lava surface was visible deep within the vent, while, at other times, the lava was mostly hidden beneath a thick crust of chilled lava on the floor of the vent. One difference, however, was the addition of a high-resolution Webcam on the rim of Halema`umau to peer into the vent. This Webcam, with low-light capabilities, has vastly improved the monitoring of the vent while offering an outstanding view of eruptive activity to the public through HVO's Web site (http://hvo.wr.usgs.gov/cams/HMcam).

With 2010 fully upon us, activity at Kīlauea's summit eruption continues to behave in what has become a fairly routine fashion. The lava surface is usually visible in the vent, though often only with a thermal camera. Small collapses still occasionally occur, and a gas plume continues to billow out and impact downwind communities with sulfur dioxide and acid particles. Despite the excitement that the summit eruption has provided, Big Islanders often long for a lasting improvement in air quality. For better or worse, we could be adjusting to what may be the new norm.

Kīlauea Activity Update

Following a three-day pause in surface flow activity due to diminished lava supply during summit deflation, breakouts resumed on March 12 as the summit reinflated and lava supply increased. These breakouts continue at the time of writing (March 18) and are situated well above the pali, about 1.6 km (1 mile) above Royal Gardens subdivision, with no current activity on the coastal plain or in the National Park.

At Kīlauea's summit, a spattering and roiling lava surface deep within the collapse pit inset within the floor of Halema`uma`u Crater was occasionally visible via Webcam during the past week. The lava surface rose significantly in response to the inflation phase of last week's deflation-inflation (DI) event, but is still deep within the vent cavity. 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-2.5 earthquake occurred at 1:41 p.m. on Tuesday, March 16, 2010, H.s.t., and was located 5 km (3 miles) northeast of Makawao, Maui, at a depth of 21 km (19 miles).

Visit our Web site (http://hvo.wr.usgs.gov) for detailed Kīlauea and Mauna Loa activity updates, recent volcano photos, recent earthquakes, and more; call (808) 967-8862 for a Kīlauea activity summary; email questions to askHVO@usgs.gov.

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Updated: March 22, 2010 (pnf)