Volcano activity of July 25, 2012 - Nevado del Ruiz, Galeras, Sotara, Popocatepetl, Sakurajima, La Garrotxa, Oyama and Novarupta (video)

This (almost) daily post intends to follow up the activity changes of volcanoes all over the world.
This post is written by geologist Rodger Wilson who specializes in Volcano seismicity and Armand Vervaeck. Please feel free to tell us about new or changed activity if we haven't written about it. -

July 25, 2012 volcano activity

Rodger is amongst us again and writes :

I have noticed that seismicity and SO2 output have increased at Nevado Del Ruiz (Colombia) during the past week. (station  OLLE).

At nearby Galeras volcano, small earthquakes and tremor continue as they have for the past year. (station ANGV)

Also in Colombia, small low-frequency earthquakes are still apparent on seismograms at Sotara volcano. (station SOSO)

To the North, eruptive activity is subdued today at Popocatepetl (Mexico) but small volcano-tectonic events and volcanic tremor affect the volcano.

Activity observed by satellites
An SO2 plume is visible over Sakurajima volcano (Japan) this morning (via the NOAA MODIS satellite imagery).

Interesting articles
Researchers Pinpoint Youngest Volcanic Area In Spain
Although volcanic scientists are able to approximate the age of lava flows, determining the exact timing of each of a volcano’s eruptions has proved difficult in the past.
A joint research team from the Universitat Autònoma de Barcelona, University of Girona, the Catalan Institute of Human Paleoecology and Social Evolution (IPHES) and other organizations has looked to establish a chronology of eruptions in the volcanic region of La Garrotxa, which contains forty volcanic cones and twenty lava flows. It is considered to be the best conserved volcanic region in the Iberian Peninsula. Read more ...

Japan island one of world's 'weirdest' places
Some 3,000 residents in Japan's Miyake-jima island must carry gas masks with them at all times as the mountains there constantly emit sulfuric gas, The Telegraph reported Tuesday. Air raid sirens go off if there is a dramatic increase in the levels of sulphur in the air, the newspaper said. The island, located 180 km from Tokyo, is dominated by Mount Oyama, an active volcano that has erupted several times in recent history. Since its most recent eruption, there has been a constant flow of sulfuric gas coming from the mountain.

Video
We have selected today a great explanatory video about the massive Alaska Novarupta explosion (Katmai National Park). The Novarupta eruption (or rather explosion) may be considered as the most powerful eruption of the 20th century (which means even more powerful than the Pinatubo or the Mt Saint Helens eruption).