VOLCANO WATCH: 'Moody' Kīlauea Volcano
This image, taken Monday, shows a description of activity along the June 27 lava flow. HVO photo.by Hawaiian Volcano Observatory
Kīlauea is a moody volcano
Trekkers to the summit were used to seeing explosions, but nothing like this. Within minutes, several hundred perished as a cloud of hot ash, fist-size rocks, and steam swept across them at hurricane velocity. Some were scorched to death and others suffocated, right along the trail they thought was safe. It was by far the worst tragedy known to have occurred at Volcano 1.
At Volcano 2, lava flows moved slowly through the forest and village, advancing here, stopping there, eventually destroying everything in their path. They presented little threat to human life, but disruption of society was high and long lasting. The on-off nature of the lava advance was inevitable for such a lava flow and nerve-racking for the villagers.
What volcanoes are these? Kīlauea and Kīlauea, one and the same volcano, acting in two very different moods. One mood is violent and explosive, the other relentless and effusive—almost a dual personality. The explosive mood caused the fatalities in 1790, and the effusive mood produced lava flows that disrupted society in the 15th, 19th, 20th, and now the 21st centuries.
How can Kīlauea experience such different moods? Its behavior has to do with the presence of a deep depression—a caldera—at the summit. Visitors today peer into the caldera, not realizing its importance in determining whether Kīlauea erupts explosively or effusively. They can be excused, because the caldera today is only a shadow of its former self. At a depth of 120 m (400 ft), it is only 20 percent or less of its past depth of at least 600 m (2000 ft).
At its deepest, the floor of Kīlauea Caldera intersects the water table, and groundwater can interact with hot magma and rocks forming the walls of the magma conduit. Water can't get in when the conduit is filled with magma. But when the conduit has emptied for some reason, water can flow into it, flash to steam, build pressure if the conduit becomes temporarily plugged by wall collapse, and finally explode. Explosions can also occur if magma erupts through a lake on the floor of the caldera.
In Kīlauea's past 2,500 years, such a deep caldera has apparently existed about 60 percent of the time, leading to two long periods of sporadic violent explosions. One lasted 1,200 years, ending in about 1000 CE; the other lasted 300 years between 1500 and 1800 CE. Tragedies such as that in 1790 can occur during these periods.
Studies show that a deep caldera forms and persists when the magma supply rate to the volcano drops to only a few percent of its value during times of effusive activity. Frequent explosions are the ultimate result. Eventually, magma supply picks up, the caldera fills, and effusive eruptions dominate, as they have for 40 percent of the past 2,500 years, most recently for the past 200 years.
Both of Kīlauea's moods have good and bad sides. In the explosive mood, the explosions take place in the caldera and can threaten life within a radius of several kilometers. The hazard is severe but local to the summit. However, falling ash can be disagreeable many kilometers away, and airborne ash from future large explosive eruptions will threaten air traffic. Such explosive periods last decades to centuries and could create economic hardship around the summit and beyond. On the other hand, ash falls contribute to soil fertility. Former settlements on Kīlauea's barren south coast were made possible by pockets of fertile ash.
In the effusive mood, the eruptions take place in the summit region and along the two rift zones. Potentially, lava flows can destroy or damage communities anywhere on the volcano. With few exceptions (for example, methane explosions and lava-delta collapses), the flows are not life-threatening but can be life-changing. Kīlauea is in an effusive mood now, and people know that it can be unpleasant.
Active volcanoes are inherently unstable, uncertain places to live. Whether in an explosive or effusive mood, Kīlauea will always present hazards to the populace. We should be realistic, but not fatalistic, about the situation. We can't command Kīlauea, but we can control our actions in the face of its hazards.
Kīlauea activity update
The lava flow from Pu'u 'Ō'ō that began on June 27 remains active. Lava continues to advance toward the northeast along the western edge of the older flow field within the Wao Kele O Puna Forest Reserve. As of Wednesday, Nov. 26, the leading edge of the flow was 5.4 km (3.3 mi) upslope from the Pāhoa Transfer Station on Apa'a Street. There was no significant change in activity at Puʻu ʻŌʻō.
The level of the summit lava lake within Halemaʻumaʻu Crater fell during the week, in concert with gradual deflation at Kīlauea's summit. As of Wednesday morning, Nov. 26, the lava lake was about 52 m (170 ft) below the rim of the Overlook crater.
Two earthquakes were reported felt on the Island of Hawai'i this past week. On Saturday, Nov.22, at 7:58 a.m., a magnitude-3.3 earthquake occurred 30 km (19 mi) northwest of Kailua at a depth of 6 km (4 mi). On Sunday, Nov. 23, at 7:35 a.m., a magnitude-3.3 earthquake occurred 2 km (1 mi) west of Volcano at a depth of 2 km (1 mi).
Visit the HVO website for past Volcano Watch articles and current Kīlauea, Mauna Loa, and Hualālai activity updates, recent volcano photos, recent earthquakes, and more; call (808) 967-8862 for a Kīlauea summary; email questions to askHVO@usgs.gov.
Japan volcano eruption hits flights
Tokyo: Flights in Japan were cancelled or diverted on Thursday to avoid a cloud of ash and smoke spewing from an erupting volcano in the south.
Japan Airlines and All Nippon Airways warned passengers of "a number of cancellations and changed destinations" on routes involving Kumamoto airport because of the 800-metre (2,600-foot) column of debris from Mount Aso.
"Today we cancelled eight flights departing from Kumamoto and four flights arriving there," a JAL spokesman said.
"There was also one flight which changed destination" to a nearby airport," he said, adding that more could be affected if the eruption worsens.
A spokesman for the airport said one international flight had been cancelled and one diverted.
Mount Aso, whose huge caldera dominates the southwestern main island of Kyushu, rumbled into life on Tuesday.
Meteorologists warned volcanic stones and ash could fall in a one-kilometre (half-a-mile) radius of the volcano.
The eruption is Aso`s first in 19 years and comes two months after Mount Ontake in central Nagano killed more than 60 hikers when it erupted without warning.
Last month, experts warned a disaster on Kyushu island, which has been struck by seven massive eruptions over the past 120,000 years, could see an area that is home to seven million people buried by molten rock in just two hours.
Lava from Cape Verde volcano threatens to engulf town
PRAIA Thu Nov 27, 2014
(Reuters) - Molten lava from a volcano in the Cape Verde archipelago slid towards the town of Cha das Caldeiras on Thursday, threatening to destroy it and a nearby village four days after an initial eruption.
Television images showed a huge lake of steaming black lava just meters away from houses in the village of Portela. The village is close to Cha das Caldeiras, whose 1,200-strong population has been evacuated to emergency shelters.
The eruption on the island of Fogo -- whose name means fire -- is the first since 1995 and the largest since 1951.
"In the last few hours, there was an increase in volcanic activity and the lava is flowing towards Portela and this community may be completely engulfed by lava," Prime Minister Jose Maria Neves said on Thursday during a visit to Fogo.
"The potential is for the total destruction of Cha das Caldeiras, one of the most fertile regions of Cape Verde," he added, calling on international aid for the country.
Experts from Portugal and the Canary Islands have already arrived to evaluate the seismic activity.
The arid, former Portuguese colony is located about 600 km (400 miles) off the coast of Senegal. Fogo's volcanic peak, surrounded by vineyards, is a favorite hiking destination.
(Reporting by Julio Rodrigues; Writing by Emma Farge; Editing by Crispian Balmer)
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