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Archive for October 11th, 2009

Rhyolitic volcanoes pack a much bigger punch

Posted by feww on October 11, 2009

Quote of the Day:

“The largest eruptions on the planet have been rhyolitic …  you might have fewer of these volcanoes, but they pack a way bigger punch.”

—Jonathan Castro of the Institut des Sciences de la Terre in Orléans, France.

30410914-072_med
Flow banding in rhyolite lava from Mono-Inyo Craters volcanic chain, California (black bands composed of obsidian). Source: USGS

Large rhyolitic volcanoes include

  • Yellowstone, Wyoming (hotspot track near the Idaho-Oregon border)
  • Long Valley, California
  • Valles, New Mexico
  • Chaiténvolcano, Chile
  • Japanese Volcanoes
  • Taupo Volcanic Zone,  New Zealand
  • Ethiopian hotspot in northeastern Africa

Chaiten - UPI
After 9,000 years of slumber, Chile’s Chaiténvolcano erupted spewing lava and ejecting ash up to 20 km into into the atmosphere, with lightning added for extra dramatic effect. (Photograph by Carlos Gutierrez/UPI,  dated May 3, 2008) . Image may be subject to copyright.

Rhyolite often erupts explosively because its high silica content results in extremely high viscosity (resistance to flow), which hinders degassing. When bubbles form, they can cause the magma to explode, fragmenting the rock into pumice and tiny particles of volcanic ash.

Rhyolite:

Rhyolite which is erupted at temperatures of 700 to 850° C, is a light-colored rock consisting of

  • Silica (SiO 2 ) content greater than about 68 percent (by weight )
  • Sodium and potassium oxides up to  about 5 percent.
  • Common mineral types include biotite, feldspar and quartz (found in a glassy matrix)

Related Links:

FEWW Volcanic Activity Forecast

Recent Posts on Chaitén:

Posted in Chaiten, Long Valley, Taupo Volcanic Zone, Valles, Yellowstone | Tagged: , , , , | Leave a Comment »

Philippines Still Flooded

Posted by feww on October 11, 2009

Image of the Day:
‘Pepeng’ [Parma] may have gone;
Floods, risk of landslides remain strong

More than a week after Parma first hit N Luzon, the roads  in central Dagupan city, northern Philippines remain flooded.


Residents wade through a flooded road brought on rains by typhoon Parma in central Dagupan city in northern Philippines October 10, 2009. REUTERS/Erik de Castro. Image may be subject to copyright.

“The most important thing is to open roads so we can send relief goods because we cannot hope to find alternate routes,” said Defense Secretary Gilberto Teodoro .

“As of now, food and relief materials can only be delivered by helicopters because it will take 2-5 days to clear up roads and bridges washed out by floods and landslides,” said Lieutenant-Colonel Ernesto Torres, of the national disaster agency.

About 500,000 tons of ready to harvest rice and other crops have been destroyed by the two storms, Ketsana and Parma, the equivalent of about 7 percent of 2009 fourth quarter forecast harvest of 6.5 million tons, said Jesus Emmanuel Paras, Agriculture undersecretary.

Various sources have estimated the cost of damage to crops and infrastructure at up to $500million.

Related Links:

Posted in Dagupan city, hantavirus, hepatitis, Ketsana, Luzon, luzon flooding, luzon landslides, Malnutrition, Manila Collapsing, Melor, Parma, Philippines, philippines floods, Philippines rain, probability of Manila collapsing, sanitation, Typhoon Melor, Typhoon Parma, Typhoons | Tagged: , , , , , , | Leave a Comment »