Exploring Kilauea's 'tiny bubbles'

For the past couple of weeks, Kilauea had presented us with a flurry of tiny earthquakes located at a shallow depth beneath the volcano’s summit. The exact cause of this cataract of miniscule events is unknown, but one possibility that comes to mind is expanding gas bubbles trying to escape from the summit magma reservoir.

Our studies at Kilauea and other volcanoes indicate that gases are a key element to understanding eruptive processes. Gases are indeed the driving force that propels molten lava at Kilauea and fine ash at Anatahan (as chronicled in last week’s Volcano Watch) to great heights.

Of the gases coming from volcanoes, carbon dioxide is the most abundant next to water vapor. Carbon dioxide, CO2, is the gas we exhale and the gas that bubbles out of soda, beer, and champagne when it’s uncorked.

On a global scale, ice-core data show that CO2 has been part of Earth’s atmosphere for at least the past 400,000 years, and studies in Hawai`i and elsewhere indicate that volcanoes played a profound role in the formation of Earth’s atmosphere during the previous 4 or more billion years.

If we visualize Kilauea’s magma chamber as a leaky balloon being filled from below, the material entering the balloon is a bubbly mixture of magma and gas coming up a narrow pipe-shaped conduit from the earth’s mantle. The pressure at the depth of the mantle is enormous, more than 28 million kilograms per square meter (40,000 pounds per square inch), owing to the weight of solid and liquid rock resting upon it. It’s like being at the bottom of a swimming pool-only, Kilauea’s pool is 10,000 meters (33,000 feet) deep instead of 4 meters (13 feet), and it’s filled with dense liquid rock instead of merely water.

As magma ascends from the mantle and enters the chamber “balloon,” pressure becomes lower because the chamber is centered a scant 4 km (2.5 miles) beneath the summit of the volcano. This lower pressure allows some of the gas, notably CO2, to bubble out in the same way uncorking a champagne bottle does.

Much of the buoyant CO2 floats to the top of the chamber and leaks out through the roof, escaping to the atmosphere through surface vents and fumaroles-more than 8,000 tonnes each day. The magma, however, almost continuously leaks out through the side of the balloon and is currently being erupted at Pu`u `O`o.

Sudden changes of magma supply or eruption rate, or of plumbing, such as the small earthquake swarm we have been observing, might accompany pressure changes within the chamber. It seems reasonable to expect that such changes would produce variations in gas discharge.

To better understand real-time changes in discharge, we have begun an intensive study to examine short-term variability of CO2 emissions at Kilauea. HVO has monitored real-time concentrations of CO2 at several locations in the summit area using small gas sensors, and we have regularly sampled and analyzed gases released from our favorite fumaroles at Halemaumau for relative CO2 levels, but this will be our first attempt to monitor the total amount of CO2 emitted on a nearly daily basis.

Measuring CO2 emission rates can be a tedious business. The data collection itself can be easy enough, but a day of measurements produces over 30,000 data points that need to be lovingly and carefully reduced to arrive at a single emission rate value for that day.

Over the next month or so, we’re hoping to produce as many CO2 emission-rate values as possible and to compare those emission rates with other measures of Kilauea’s activity such as other geochemical data, earthquakes and ground surface deformation measurements. Whether Kilauea cooperates extravagantly by providing some significant geophysical event, such as an earthquake swarm or summit tilt event, is of secondary importance. We’ll be happy just watching the tiny CO2 bubbles pop at the top of this beautiful volcanic champagne glass.

Activity Update

Eruptive activity at the Pu`u `O`o vent of Kilauea Volcano continued unabated during the past week. A new breakout above Pulama pali is feeding a flow on the east side of the main Mother’s Day flow. The new flow has worked its way halfway down Pulama pali and is providing visitors a great view at night. Discontinuous incandescent patches outline the trace of the main Mother’s Day flow tube system on Pulama pali. Surface breakouts occur near the base of Paliuli and just above the Highcastle sea cliff. The Highcastle delta has multiple ocean entries and is slowly expanding seaward.

The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying sudden collapses of the new land. The steam clouds are highly acidic and laced with glass particles. The National Park Service has put warning signs in critical places. Do not venture beyond these signs and onto the lava deltas and benches.

Residents throughout Kona and one in Ahualoa felt an earthquake at 3:55 a.m. on June 8. The magnitude-3.7 temblor was located 47 km (29 mi) southwest of Honaunau at a depth of 43 km (26 mi).

Mauna Loa is not erupting. The summit region continues to inflate slowly. Seismic activity remains low, with only three earthquakes located in the summit area during the last seven days.

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