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Volcano activity of July 31, 2012 - 99 volcanic earthquakes since July 11 at Mt. Tongariro volcano, New Zealand + Etna

This (almost) daily post intends to follow up the activity changes of volcanoes all over the world.
This post is written by geologist Richard 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. -

Update August 6
Please check also our August 6 article for the eruption of Mount Tongariro.

July 31, 2012 volcano activity

GNSC science volcanologist Michael Rosenberg published a rather extensive report on the current Mt. Tongariro volcano activity earlier today.

As part of our routine monitoring, we have recorded a sequence of volcanic earthquakes at Mount Tongariro since July 13, peaking in activity on July 20, and now numbering 3-10 per day, as shown on the graph below. The earthquakes cluster in a zone between Mount Tongariro and the eastern side of Lake Rotoaira at 2-7 km depth. These are very small earthquakes and unlikely to be felt by people.

To better understand the significance of these earthquakes and if volcanic unrest is developing at Mount Tongariro we have recently:

  • conducted more sampling of selected springs and fumaroles and completed some chemical analyses;
  • installed a GPS instrument to detect possible ground movement.

Analysis of the gas samples collected in the last fortnight shows that volcanic gas levels are above the normal levels measured at Tongariro. There is always a mix of volcanic and hydrothermal gases and fluids rising to the surface at Tongariro, but the recent samples contain a marked increase in the volcanic gas component. These results confirm the volcanic unrest indicated by the seismic data.

We are working to complete the analysis of the water samples and plan more field work within the next two weeks or sooner if activity changes significantly. GNS Science volcanologists are monitoring the unrest and further information will be released as necessary.

Mount Tongariro is a volcanic complex that lies to the north of Mount Ngauruhoe. It consists of numerous craters, cones and lava flows. Te Māri craters lie about two kilometers east of Ketetahi hot springs on the north side of Mount Tongariro. The Te Māri craters are the last craters to be active on Tongariro. Ash eruptions from Tongariro are recorded from 1855 to 1897, as well as unconfirmed activity in 1926-27.

Text and graphics courtesy Geonet and GNS Science

Rodger Wilson daily volcano activity overview :

The volcanoes we watch seem to be "on hold" for the time being.
Popocatepetl volcano (Mexico) has maintained an average of less than one exhalation of gas and ash per hour the past week.  I have not included the Popo seismogram today due to a software "glitch" which renders the seismogram useless.

In Guatemala, tremor appears to be subsiding at Fuego volcano (FG3), while rockfalls and degassing events are frequent on seismograms at Santa Maria volcano (STG3).

Tremor (and gas output) are up at Nevado Del Ruiz today (Colombia). (station OLLE)

Seismicity at Mt Tongariro volcano (New Zealand) has returned to low levels, but numerous small events are evident on seismic records there.

Nuevo Bocca at Etna volcano, Sicily, Italy showed last night some higher activity as can be seen on the volcanic earthquakes graph below. ER reader Nataly recorded some snapshots from a webcam showing the nightly activity. This is however no paroxysm which we often see at Etna volcano. (graphics courtesy INGV and Lave Webcam)
Update 15:48 UTC : Volcanic earthquakes are gradually increasing

Etna volcano (Nuevo Bocca ) activity during the evening hours of July 30 2012