Volcano Watch — Mayon Volcano could be gearing up for explosive activity

Scientists from the Philippine Institute of Volcanology (PHIVOLS), who have been monitoring activity at Mayon closely since it started emitting ash in mid-July, are concerned that the current activity is just the lead-in to a more explosive-and destructive-eruption.

Bulkang Magayon-Mayon Volcano-is well known for its beauty and nearly perfectly symmetrical cone. This classic, conical stratovolcano shape is the result of eruptions of viscous lava flows from a central vent at the summit of the volcano. Eruptions are frequent enough at Mayon, the most active volcano in the Philippines, to overcome erosive forces that quickly modify the slopes of most volcanoes.

Many of Mayon's eruptions have resulted in numerous fatalities of people living on its slopes, most due to fast-moving pyroclastic flows and lahars-mixtures of volcanic material and water-engulfing their homes and villages.

Lahars were also responsible for widespread destruction during and after the 1991 Pinatubo eruption in the Philippines. In the sequence of events that led up to the cataclysmic explosion at Pinatubo, one of the recognized precursory signals was a large increase in the amount of volcanic gas emitted from the volcano. The copious amount of gas, along with increased seismicity and rapidly changing shape of the volcano, indicated that a large amount of magma was accumulating at shallow levels.

Gas emissions dropped precipitously a month later. Far from being reassured by the sudden drop, PHIVOLCS and USGS scientists recognized that this signaled a sealing-off of the pathways for the gas to escape, and that internal pressure was building to very dangerous levels. The explosive eruption that soon followed devastated the surrounding towns and sent tons of ash and sulfur dioxide into the atmosphere, vividly coloring our sunsets for years.

Is this a likely scenario for Mayon? The gas emissions hold important clues at explosive stratovolcanoes, because the viscous, pasty magma does not easily allow gas to leave, and pressures can build up until the volcano blows its top. In contrast, Hawaiian magma is far more fluid, so it is easier for gases to escape to the surface.

While large amounts of volcanic gas are being emitted from Mayon, the measured amounts have been variable, and there have apparently been discrepancies between various measurement systems. Thus it has been difficult to evaluate how much magma may be poised to erupt.

Hawaiian Volcano Observatory staff may soon travel to Mayon to help assess the gas emissions measurements with our equipment.

This collaboration continues a long-standing relationship between PHIVOLCS and the Hawaiian Volcano Observatory. Besides assisting in the response to the unrest and volcanic crisis at Pinatubo, HVO staff helped set up monitoring networks during Mayon's 1984 eruption.

We hope that HVO can be of assistance to the Philippine volcanologists and that the current eruption at Mayon does not build to explosive levels.

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Volcano Activity Update

This past week, activity levels at the summit of Kīlauea Volcano have remained at background levels. The number of earthquakes located in the summit area is low (usually less than 10 per day that are large enough to locate). Widening of the summit caldera, indicating inflation, has resumed after pausing earlier in April. We continue to monitor unusual inflation south of Halema`uma`u Crater.

Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from several vents within the crater. Lava continues to flow through the PKK lava tube from its source on the flank of Pu`u `O`o to the ocean. In the last week, the only surface flow activity was along the margins of the "Campout flow," which entered the ocean at East Ka`ili`ili two weeks ago. The lava bench at East Ka`ili`ili is now over 500 m (1,650 ft) long by 50 m (165 ft) wide, with an area of about 1.7 ha (4.3 acres). As of August 16, the new ocean entry, which is located 7.8 km (4.7 mi) from the end of Chain of Craters Road, was still active.

Lava is still entering the ocean at East Lae`apuki, also in Hawai`i Volcanoes National Park. The lava bench has refilled most of the gap left by the partial collapse on July 30 and has a total surface area of about 22 ha (55 acres).

Access to the sea cliff near the ocean entries is closed, due to significant hazards. The National Park has reopened the surrounding area, however. 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 no earthquakes beneath Hawai`i Island reported felt within the past week.

Mauna Loa is not erupting. During the past week, earthquake activity remained low beneath the volcano's summit (three earthquakes were located). Extension of distances between locations spanning the summit, indicating inflation, continues at slow rates. Visit our web site for daily Kīlauea eruption updates and nearly real-time Hawai`i earthquake information.