**************************************************************** From: James P Kauahikaua <jimk@xxxxxxxx> **************************************************************** Sloshing lava lake viewed within Halema`uma`u vent For the first time since the new vent opened in Halema`uma`u Crater on March 19, HVO scientists in a helicopter hovering over the crater were able to see the surface of a sloshing 50 m (160 ft) diameter lava lake about 100 m (330 ft) below the vent rim. HVO scientists have speculated that a lava pond existed a few hundred meters below the vent, but have not been able to get visual confirmation until this morning. A second viewing early this afternoon revealed a roiling pond with multiple bursting bubbles changing into a central upwelling circulation pattern. The lake level dropped slightly before the cycle restarted. This behavior has been witnessed before, most recently in Pu`u `O`o vents and the July 21 lava ponds on Kilauea's east rift zone, and is known as 'gas pistoning.' One model explains pistoning as small gas bubbles coalescing into larger bubbles beneath a crust on a lava pond, rising to the surface, and then bursting. The released pulse of hot gas carries rock dust from the collapsing vent walls, bits of the lava lake crust, and small amounts of spatter. The Halema`uma`u vent has produced six significant explosive eruptions in the past 5.5 months, most recently on September 2, 2008 at 8:13 p.m. H.s.t., during which noteworthy amounts of fresh lava spatter and lithic material (rock fragments and dust) were ejected on to the crater rim. Just prior to this event, incandescence from the vent was almost nonexistent except for brief pulses of glow. Nearly eight hours later, Kilauea's summit abruptly inflated, signaling the end of 39 hours of deflation. Summit deflation-inflation (DI) events have been observed at least 20 times since the Halema`uma`u vent opened. Each DI event has been interpreted as the fall and subsequent rise in magma levels beneath the summit. Less than 8 hours after inflation started, episodic tremor bursts began which are visible at night as pulses of bright incandescence every 5-6 minutes. Episodic tremor bursts have been a nearly constant feature of the Halema`uma`u vent over the past few months and were one of the early pieces of evidence pointing toward a gas pistoning source. This unusually bright incandescence over the past two nights and the volume of material erupted on September 2 are consistent with a lava surface at relatively shallow depths beneath the vent. Molten lava is not directly visible from the Jaggar Museum overlook, but that vantage point provides excellent views of the glowing vent at night. Jim Kauahikaua, Scientist-in-Charge USGS Hawaiian Volcano Observatory ============================================================== To unsubscribe from the volcano list, send the message: signoff volcano to: listserv@xxxxxxx, or write to: volcano-request@xxxxxxxx To contribute to the volcano list, send your message to: volcano@xxxxxxxx Please do not send attachments. ==============================================================
