May 24, 2001
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
An exciting couple of weeks at Kilauea
The last couple of weeks have been exciting ones to be studying active volcanism in Hawai'i. To start with, after several months of fairly constant effusion of lava and gas, emissions of sulfur dioxide gas (SO2) doubled, seemingly overnight, then tripled over the next few days. The SO2 that is eventually released from Kilauea is dissolved in the magma--like gas bubbles dissolved in champagne. Increased gas emissions from the magma are usually associated with an increased supply of magma to the eruption. Sure enough, the increased gas emissions observed over the past weeks were accompanied by renewed pond activity within Pu'u 'O'o's crater for the first time in months, indicating that more magma was moving through the system.
Last Sunday evening, several of the staff from HVO and the National Park had an impromptu gathering at the observatory to puzzle over Kilauea's latest developments. It had been an exciting afternoon; within a little over an hour-much less time than even a Kilauea heartbeat-- a tiltmeter at the summit of the volcano near HVO suggested that a volume of up to four million cubic meters (mcm), (five million cubic yards (mcy)) of excess magma had entered and inflated the summit magma reservoir of the volcano. For perspective, a ready-mix truck holds about seven cubic meters (nine cubic yards) of concrete.
About 20 minutes later, Pu'u 'O'o cone also began swelling in a similar manner. While this was happening, the magnitude of seismic tremor (very low-level ground shaking associated with magma movement) beneath the summit and Pu'u 'O'o increased as well. We were impressed by the four mcm (five mcy) of magma, because this is a typical amount supplied to the eruption over the course of ten days-- not an hour! Among our several questions was: "If this much excess magma was intruding the summit reservoir and not being erupted, where would it go within the volcano, and what would happen next?"
In nearly as short a time period as the inflation had occurred, one of our questions was answered. The summit tilt reversed, and a few hours later, instruments located on the rim of Pu'u 'O'o indicated that new lava was pouring onto its crater floor. Inflation and tremor at the cone and beneath Kilauea's summit subsided thereafter, and the HVO staff decided to go home and get some sleep. The pressure was literally off, or at least relieved.
By the next day (Monday), eruptive activity and gas emissions from the east rift seemed to be returning to normal. On Tuesday, however, no lava was visible except that draining from tubes at the coast, and we thought the eruption might be heading into a pause. This turned out to be only a temporary slow-down, not a stoppage. By Wednesday morning, lava had reappeared on Pulama pali, and by the afternoon, field crews reported vigorous breakouts of lava above the pali between the 2,300 - to 2,200- foot elevations.
This is hardly the end of even this episode of the story. As of this writing, Thursday afternoon, one of our original questions of last Sunday night remains: Where did the four million cubic meters (five mcy) of excess magma go? Although we did see increased lava effusion at Pu'u 'O'o and on the flow field, we are confident that the amount of lava erupted over the last week was much less than this. And so, if you happen upon an extra several million cubic meters of magma (several million cubic yards), it should still be hot, so don't touch it, but please return it to Kilauea. Some of us are still looking for it. But most likely, you won't find it, because it is probably stored below Pu'u 'O'o in space made available as the south side of Kilauea moves away from the rest of the volcano.
As mentioned above, eruptive activity of Kilauea Volcano fluctuated during the past week, and the volume of lava entering the ocean east of Kupapa`u reflected this fluctuation. The surge in lava production on Wednesday overwhelmed the tube system and resulted in three major breakouts. Surface flows provide visitors at the end of the Chain of Craters road in Hawai`i Volcanoes National Park a great display of lava cascading down Pulama pali.
One earthquake was reported felt during the week ending on May 24. A resident of Pahala felt an earthquake at 4:26 p.m. on May 24. The magnitude-3.2 earthquake was located 4 km (2.4 mi) east of Pahala at a depth of 10.7 km (6.4 mi).
The URL of this page is http://hvo.wr.usgs.gov/volcanowatch/archive/2001/01_05_24.html
Updated: May 29, 2001 (pnf)