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September 23, 1999

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

Kilauea's Pause That Refreshes -- Kailua-Kona, that is

One of the ways we monitor Kilauea's activity is by studying the release of volcanic gases. Gases like sulfur dioxide and carbon dioxide are trapped (dissolved) in magma at depth, where pressures within the Earth's crust and mantle are very great-many thousands of pounds per square inch. When magma rises up and is erupted at places like Pu`u `O`o, the pressure is decreased and some of the gas escapes. Anyone who has shaken, quickly opened, and then poured a bottle of soda out into a glass has had an instructive lesson in what dissolved gas can do.

At Kilauea, as long as the volcano is pouring lava out of its vents, the gas continues to bubble out-more erupting lava means more erupting gas. So much gas, in fact, that Kilauea ranks number one on the nation's list of stationary emission sources for noxious sulfur dioxide (SO2 ), a regulated pollutant. This gas is the one responsible for the biting, choking odor you smell just after lighting a kitchen match. When Kilauea is actively erupting, it emits about 2000 tonnes of SO2 each day-enough to fill 100 Goodyear blimps. Although other stationary SO2 emission sources in the nation, such as coal-fired power plants, are working hard to curb their emissions, Kilauea for the most part, has persistently poured out its emissions of both gas and lava-until two weeks ago, that is.

As we described in the September 19 Volcano Watch, early on the morning of September 12 a disturbance in Kilauea's plumbing system was evidenced by a rapid deflation of the summit and east rift zone, and a swarm of small earthquakes that outlined an intrusion of magma in the rift zone. This diversion of magma from the supply line feeding Pu`u `O`o sent the eruption into a pause of surface activity.

The effects of the pause were widespread. With very little magma flowing into its eruptive conduit, the crater floor of Pu`u `O`o collapsed, dropping about 30 m (100 ft) and shaving a few meters off the height of the cone as well. Without lava flowing through the tube system, the coastal entry ceased activity, and 2 hectares (5 acres) of the island's newest land calved off into the ocean.

Since no new lava was being erupted beginning on September 12, very little gas was released either. SO2 emissions from Pu`u `O`o declined from about 1500 tonnes/day just before the pause to around 40 tonnes/day during the pause. The gas coming from Pu`u `O`o was bubbling out of the top of a relatively stagnant magma column at the bottom of the crater. With less SO2 coming out, less vog (volcanic smog) could be formed by the reaction of released gas with air, moisture, and sunlight.

For residents and visitors to the leeward side of the island, this truly has been the pause that refreshes. We at HVO received grateful phone calls informing us that Ka`u and Kona residents could actually see the horizon and blue skies again. For those of us in east Hawaii, however, air quality changed little since trade winds held steady and carried what small amount vog there was toward the leeward side of the island.

Over the past two weeks, we measured fairly steady inflation of Kilauea's summit, which exceeded its pre-pause level. As this article is going to press, activity is resuming at a recharged and refreshed Kilauea. Lava is beginning to reoccupy the upper part of the tube system, and SO2 emissions from Pu `u `O`o have climbed nearly 10-fold, approaching the pre-pause level. It is too early to tell just yet, but historically, longer eruptive pauses are followed by more surface lava flows than are short pauses. This is because, during long pauses, there is more time for the lava tube system to cool and cave in, making it difficult for lava to flow through the tube.

So, while the "pause that refreshes" temporarily suspended Kilauea's title as the number one emission source in the nation for SO2 , we volcano-enthusiasts are experiencing an exciting resumption of activity. It's the Real Thing!

Eruption Update

From September 12 to noon on Thursday, September 23, eruptive activity of Kilauea Volcano was confined to a sluggish pool of lava within Pu`u `O`o Crater. Shortly after noon on September 23, lava was observed flowing in the tube system below Pu`u `O`o. The lava is within the old, established tube system down to the 675 m (2200 ft.) elevation where it leaves the tube and becomes a pahoehoe flow. The pahoehoe flow is slowly moving toward the top of Pulama Pali as it fills low spots along the way. When the flow starts to cascade over the pali, visitors at the end of the Chain of Craters road in Hawaii Volcanoes National Park will have a spectacular view. The flow will eventually form a new tube or reenter the old tube system as it makes its way to the ocean.

An early riser in Hilo reported feeling an earthquake at 3:27 a.m. on Friday, September 17. The magnitude-2.8 temblor was located 3 km (1.8 mi) east of Wainaku at a depth of 36.9 km (22.1 mi). A magnitude-3.5 earthquake was reported felt in the Kilauea summit region at 9:58 a.m. on September 18. The earthquake was located in the upper east rift zone of Kilauea at a depth of 3.0 km (1.8 mi).

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Updated: 4 Oct 1999