June 28, 2007

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

Magma, magma, who’s got the magma?

View of Pu‘u ‘O‘o

Last week’s Volcano Watch described HVO’s most recent and exciting challenge: to figure out what might happen next with Kilauea’s marked change in eruptive activity. It is often through change that we learn and grow in our understanding of life. The same idea is certainly true for the study of volcanic processes. Eruptive changes provide some of the best opportunities to better understand how volcanoes “live.”

Philosophy aside, HVO staff members are pretty jazzed right now about what’s happening at Kilauea. One of this week’s big questions is a twofold one: Where is the magma going and how might it re-emerge?

To briefly recap the event, Kilauea’s 24-year-old ongoing eruption was disrupted early on Father’s Day by a swarm of earthquakes in the upper east rift zone, indicating that magma was intruding in a new area near Kane Nui o Hamo, just east of Mauna Ulu. Within several days, the rift zone in the intrusive area spread apart nearly a meter (3 feet).

Lava broke the surface, forming two small flows that covered an area of about 0.8 hectares (2 acres) before stopping abruptly. The intrusion and extrusion processes drained a substantial amount of magma from Kilauea’s summit reservoir and appeared to have also nearly stopped the supply to Pu`u `O`o. The cone’s crater floor collapsed, leaving a gaping maw at least 100 meters (330 feet) deep. Its lava tubes have drained, and flows are no longer entering the ocean.

Overall, gas emissions from the volcano have declined as well. Sulfur dioxide, the gas principally responsible for the nearly ubiquitous vog in Ka`u and Kona, has dropped by about 75 percent, and HVO has begun receiving phone calls of appreciation for the improved air quality in these districts.

One mystery right now, though, is the disparity between how much magma we believe is still entering the volcano from the mantle, and the fact that no new lava and very little gas has been erupted at the surface for over a week.

Several studies of Kilauea’s long-term behavior conclude that magma is supplied to the volcano at a fairly consistent rate of between 0.1 and 0.2 cubic kilometers (0.024 to 0.48 cubic miles) per year. This amount, as erupted lava, could fill between 100 and 200 Olympic-sized swimming pools (OSP) each day. For the past 24 years, Kilauea has eschewed the Olympic pools, but instead, has favored resurfacing nearly 120 square kilometers (46 square miles) of the island, and has added an additional 202 hectares (500 acres) to Hawai`i.

So if magma is still being supplied at a rate of 100 OSPs per day, where is it going, and what might happen next? The short answer is that the intrusion and eruption of lava on the upper east rift rapidly depleted Kilauea’s summit reservoir of the volume of magma required to produce the intrusion and the small associated surface flow. Because of this geologically “momentary” depletion, the reservoir will take some time to refill.

We don’t know yet precisely how much magma is tied up in the new intrusion. Ground-based and space-base measurements and modeling will help refine estimates of this quantity. However, studying past events like this one indicates that Kilauea has already recovered roughly 25 percent of the deflation that occurred in the summit area during the event.

Still, the science of eruptive processes is not always straightforward. Magma supply rate and lava eruption rate are often not quite equal. And while volcanologists studying Kilauea, mostly agree that magma supply to the volcano has been steady in the long term (tens to hundreds to thousands of years), shorter term variations do occur.

Within the past several years, for example, Kilauea showed signs—increased expansion and gas release—that a short term magma supply increase had occurred. With such supply rate perturbations comes the interplay between getting magma into the volcanic edifice and having it affect eruptive processes. Time will tell what the very immediate subsurface changes will actually bring in terms of surface expression.

The eruptive changes occurring now at Kilauea are unmistakably helping HVO scientists better understand and appreciate the wonders of this young volcano’s life. In that same spirit, we at HVO would like wish two of our younger staff members, Sara Abraham and Kevan Kamibayashi, our best wishes for growth as they experience a change in their lives together this week by becoming newlyweds. Aloha Nui Loa, Sara and Kevan!

Activity update

Pu`u `O`o is no longer erupting, and there are no active surface flows anywhere on the flow field or at the coast. This is the first eruptive pause since December 15, 2000. A small pad of lava that was erupted on the northeast flank of Kane Nui o Hamo shield early on June 19 was only active for a few hours. There has been no continuation or resumption of activity in this area. The output of steam and fume from ground cracks near this new flow, and from cracks west of the base of Kane Nui o Hamo shield, has decreased and is now barely visible.

Only one earthquake beneath Hawai`i Island was reported felt within the past week. A magnitude-2.9 earthquake occurred at 6:15 p.m. H.s.t. on Wednesday, June 27, and was located 15 km (9 miles) west northwest of Kawaihae at a depth of 16 km (10 miles). Mauna Loa is not erupting. Two earthquakes were located beneath the summit area in the past week. Extension between locations spanning the summit, indicating inflation, continues at steady, slow rates which have slowed further since May 2007.

Visit our Web site (hvo.wr.usgs.gov) for daily Kilauea eruption updates and nearly real-time Hawai`i earthquake information.

This article was written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.