Volcanoes under pressure

November 15, 2019

When will the next eruption take place? Examination of samples from Indonesia's Mount Merapi show that the explosivity of stratovolcanoes rises when mineral-rich gases seal the pores and microcracks in the uppermost layers of stone. These findings result in new possibilities for the prediction of an eruption.

Mount Merapi on Java is among the most dangerous volcanoes in the world. Geoscientists have usually used seismic measurements which illustrate underground movements when warning the population of a coming eruption in time.

An international team including scientists from the Technical University of Munich (TUM) has now found another indication for an upcoming eruption in the lava from the peak of Mount Merapi: The uppermost layer of stone, the "plug dome", becomes impermeable for underground gases before the volcano erupts.

"Our investigations show that the physical properties of the plug dome change over time," says Prof. H. Albert Gilg from the TUM Professorship for Engineering Geology . "Following an eruption the lava is still easily permeable, but this permeability then sinks over time. Gases are trapped, pressure rises and finally the plug dome bursts in a violent explosion."

Mount Merapi as a model volcano

Using six lava samples, one from an eruption of Mount Merapi in 2006, the others from the 1902 eruption - the researchers were able to ascertain alterations in the stone. Investigation of pore volumes, densities, mineral composition and structure revealed that permeability dropped by four orders of magnitude as stone alteration increased. The cause is newly formed minerals, in particular potassium and sodium aluminum sulfates which seal the fine cracks and pores in the lava.

The cycle of destruction

Computer simulations confirmed that the reduced permeability of the plug dome was actually responsible for the next eruption. The models show that a stratovolcano like Mount Merapi undergoes three phases: First, after an eruption when the lava is still permeable, outgassing is possible; in the second phase the plug dome becomes impermeable for gases, while at the same time the internal pressure continuously increases; in the third phase the pressure bursts the plug dome.

Photographs of Mount Merapi from the period before and during the eruption of May 11, 2018 support the three-phase model: The volcano first emitted smoke, then seemed to be quiet for a long time until the gas found an escape and shot a fountain of ashes kilometers up into the sky.

"The research results can now be used to more reliably predict eruptions," says Gilg. "A measurable reduction in outgassing is thus an indication of an imminent eruption."

Mount Merapi is not the only volcano where outgassing measurements can help in the timely prediction of a pending eruption. Stratovolcanoes are a frequent source of destruction throughout the Pacific. The most famous examples are Mount Pinatubo in the Philippines, Mount St. Helens in the western USA and Mount Fuji in Japan.
-end-
Contact

Prof. Dr. H. Albert Gilg
Technical University of Munich
Professorship for Engineering Geology
agilg@tum.de

Technical University of Munich (TUM)

Related Volcano Articles from Brightsurf:

Using a volcano's eruption 'memory' to forecast dangerous follow-on explosions
Stromboli, the 'lighthouse of the Mediterranean', is known for its low-energy but persistent explosive eruptions, behaviour that is known scientifically as Strombolian activity.

Rebirth of a volcano
Continued volcanic activity after the collapse of a volcano has not been documented in detail so far.

Optical seismometer survives "hellish" summit of Caribbean volcano
The heights of La Soufrière de Guadeloupe volcano can be hellish, sweltering at more than 48 degrees Celsius (120 degrees Fahrenheit) and swathed in billows of acidic gas.

Researchers reveal largest and hottest shield volcano on Earth
Researchers from the University of Hawai'i at Mānoa revealed the largest and hottest shield volcano on Earth--Pūhāhonu, a volcano within the Papahānaumokuākea Marine National Monument.

Formation of a huge underwater volcano offshore the Comoros
A submarine volcano was formed off the island of Mayotte in the Indian Ocean in 2018.

Volcano F is the origin of the floating stones
Since August a large accumulation of pumice has been drifting in the Southwest Pacific towards Australia.

Researchers discover a new, young volcano in the Pacific
Researchers from Tohoku University have discovered a new petit-spot volcano at the oldest section of the Pacific Plate.

What happens under the Yellowstone Volcano
A recent study by Bernhard Steinberger of the German GeoForschungsZentrum and colleagues in the USA helps to better understand the processes in the Earth's interior beneath the Yellowstone supervolcano.

Geoengineering versus a volcano
Major volcanic eruptions spew ash particles into the atmosphere, which reflect some of the Sun's radiation back into space and cool the planet.

How to recognize where a volcano will erupt
Eleonora Rivalta and her team from the GFZ German Research Centre for Geosciences in Potsdam, together with colleagues from the University Roma Tre and the Vesuvius Observatory of the Italian Istituto Nazionale di Geofisica e Vulcanologia in Naples have devised a new method to forecast volcanic vent locations.

Read More: Volcano News and Volcano Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.