Volcano Watch — Here's the dirty truth about mud volcanoes

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As residents of Hawai`i, we are, for the most part, acutely aware of volcanic processes and products. This is especially true for those of us living on the Big Island, where thoughts of volcanic eruptions and lava flows are always lurking in the backs of our minds. This is what history and personal experience do for us.

mud bubbling with escaping natural gas

Piparo, on the island of Trinidad's mud eruption. Escaping natural gas, with an oil scum on water.

(Public domain.)

It is unlikely, however, that these same thoughts ever crossed the minds of the people living in the tiny farming community of Piparo, on the island of Trinidad in the southern Caribbean Sea. That is, not until February 22, 1997, when a volcano erupted in the midst of their village, crushing roofs and burying houses in mud. Fortunately, the rumbling and shaking that preceded the eruption warned the villagers, who escaped before their houses were destroyed.

A similar case occurred outside Baku, the capital of Azerbaijan, in south-central Asia, on October 25, 2001. There, without warning, an eruption blasted flames nearly 1,000 feet into the air and blanketed the surrounding area with tons of mud. Luckily, again, there were no injuries.

What is surprising about these events is that neither Trinidad nor Azerbaijan has volcanoes in the traditional sense of the word - that is, volcanoes driven by magmatic processes. What Trinidad and Azerbaijan have, instead, are mud volcanoes, a strange and relatively obscure geologic feature found on nearly every continent worldwide, as well as in near-shore environments.

Though poorly understood, mud volcanoes are found where subsurface layers of fluidized sediments, like silt and clay, have been pressurized by tectonic activity, such as at the boundaries of the earth's crustal plates, or by the accumulation of hydrocarbon gases. This pressurized sediment is forced upward, where it erupts on the earth's surface to form conical mounds of mud.

Most of these mud volcanoes are small, from only a few inches to several feet high, but some, such as a few of those in Azerbaijan, are more than six miles in diameter and several hundred feet high. Though mud volcanoes do sometimes erupt with powerful results, they are, for the most part, harmless. Gases bubble passively from the tiny "craters" at their summit, and upwelling mud slowly oozes out to form small flows. Mud volcanoes are also different from the bubbling mud pots found in active geothermal areas, such as in Yellowstone Park. The mud that erupts from mud volcanoes is cold, or perhaps only slightly warmer than the ambient ground temperature.

When large explosions do occur, they are thought to be caused by the accumulation of hydrocarbon gases, such as methane. Spontaneous combustion of these gases can lead to devastating results. Once the pressure is released, however, the mud volcano returns to a passive state, perhaps not becoming explosive again for decades or centuries, if ever.

The mud that is extruded from mud volcanoes can rise from as deep as several miles. Because mud volcanoes are also often associated with hydrocarbons, they provide useful information on the geology and petroleum potential of deep sedimentary basins. However, since the dominant gases expelled from mud volcanoes are methane and CO<SUB>2</SUB>, mud volcanoes are also considered an important source of greenhouse gases. With at least 1,100 mud volcanoes on land, and perhaps as many as 100,000 more underwater, it is estimated that as much as 185 million pounds of greenhouse gases may escape from mud volcanoes each day. Though the amount is tiny when compared to industrial sources worldwide, this is still a significant amount of gas.

Despite the attention that magmatic volcanoes receive, both by the scientific community and the media, their mysterious muddy cousins are unique features not to be overlooked.

Volcano Activity Update

Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from several vents within the crater and on the southwest side of the cone. Lava continues to flow through the PKK lava tube from its source near Pu`u `O`o to the ocean, with only a few surface flows breaking out of the tube. Flows are visible intermittently on the steep slope of Pulama pali. As of October 13, lava is entering the ocean at East Lae`apuki, in Hawai`i Volcanoes National Park.

Small bench collapses continue to occur at the ocean entry. Large cracks cross both the old and new parts of the bench. Access to the ocean entry and the surrounding area remains closed, due to significant hazards. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

There were five earthquakes reported felt on Hawai`i Island within the past week. The first four occurred in a flurry of more than a dozen earthquakes beneath the northeast rift zone of Mauna Loa all about 15 km (9 miles) east of the summit at a depth of 7 km (4 miles). The cluster of felt earthquakes occurred in rapid succession, starting with a magnitude-3.8 at 11:45 p.m. on Sunday, October 9, and ending with a magnitude-2.5 14 minutes later. The fifth felt quake occurred at 6:29 p.m. on Tuesday, October 11 and was located 11 km (7 miles) northwest of Ka`ena Point on Kīlauea Volcano at a depth of 9 km (6 miles) p.m.

Mauna Loa is not erupting. During the past week, the count of earthquakes located beneath the volcano remains at low levels. Inflation continues.