February 11, 2010
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Lava advances in ?two steps forward, one step backward? style
Long-time Kīlauea Volcano watchers know the drill when the supply of magma to the active vent on the volcano?s east rift zone is interrupted—abandonment of the ?old? lava tube system, breakout of new surface flows, an evolving tube network, and eventually a new ocean entry.
This drama is unfolding again as many small 'a'ā and pahoehoe flows spread through what is left of the Royal Gardens subdivision and move a short distance across the coastal plain. The flows are providing sporadic, distant views of incandescent lava, glow, and burning vegetation from the Hawai`i County viewing area in Kalapana.
These flows are the consequence of a temporary decrease in magma supply to the active vent, beginning December 29 and lasting nearly 6 days. The decrease corresponded to a pronounced deflation of the summit and east rift zone area, followed by several days of only slight inflation as recorded by sensitive tiltmeters.
Scientists interpret deflation as an indicator of a relative decrease in magma supply and inflation as an increase in magma supply.
When the December 29 deflation event began, lava was pouring into the ocean at Waikupanaha, and more than 1,000 people per day were visiting the Hawai`i County lava viewing area. Within a few days, however, the entry shut off completely. Lava stopped entering the ocean by January 4, but some lava continued to move through the uppermost part of the tube system within about 3 km (2 miles) of the TEB vent.
The upper tube system lies within a complex series of rootless shields tens of meters (yards) tall that were built by thousands of overlapping small flows between November 2007 and February 2008. Near the lower end of these rootless shields, the original tube system became blocked as the Waikupanaha entry shut off, forcing lava to break out onto the surface at several locations between the shields and the top of Royal Gardens.
These flows are slowly creating a new but unstable tube system as the supply of magma to the vent continues to fluctuate. Seven deflation-inflation events have occurred since December 29.
During the inflation periods, new breakouts from the tube have generally formed longer flows that reached lower and lower elevations on the pali. Breakouts from the next inflation period often start lower than the previous breakout—evidence that the tube system was elongating and forming longer flows. The overall result of this pattern, as described by scientists, is a ?two steps forward, one step back?-style of flow advancement and tube development.
Continued small fluctuations in magma supply as a consequence of small deflation-inflation cycles will likely promote growth of the new tube system all the way to the coast, west of the Waikupanaha entry. But a larger- or longer-than-usual deflation event may cause the young tube system to stagnate and trigger new breakouts above Royal Gardens in a sudden step backward.
Kīlauea Activity Update
Surface flows have been active on the lower pali and coastal plain within the Royal Gardens subdivision. These flows have largely stayed close to the base of the pali but had extended halfway to the coast by Thursday morning. A deflation/inflation cycle, which started on Tuesday at Kīlauea's summit, caused these flows to slow down by mid-week. Surface flows in the same general area will likely be renewed when the volcano re-inflates.
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 sporadically visible via Webcam. On several occasions, the lava surface rose slightly briefly covering the floor of the pit, but activity, for the most part, has remained fairly steady. Volcanic gas emissions remain elevated, resulting in high concentrations of sulfur dioxide downwind.
There were no felt earthquakes during the past week.
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.
Updated: February 16, 2010 (pnf)