Repeatedly throughout Earth's history, giant pools of magma greater than 100 cubic miles in volume have formed a few miles below the surface.
They are the sources of super-eruptions - gigantic volcanic outbursts that throw 100 times more superheated gas, ash and rock into the atmosphere than run-of-the-mill eruptions, enough to blanket continents and plunge the globe into decades-long volcanic winters.
The most recent super-eruption took place about 27,000 years ago in New Zealand, well before humans kept records of volcanic eruptions and their aftermath. Geologists today are studying deposits from past super-eruptions to try and understand where and how rapidly these magma bodies develop and what causes them to eventually erupt. Despite considerable study, geologists are still debating how quickly these magma pools can be activated and erupted, with estimates ranging from millions to hundreds of years.
Now a team of geologists have developed a new "geospeedometer" that they argue can help resolve this controversy by providing direct measurements of how long the most explosive types of magma existed as melt-rich bodies of crystal-poor magma before they erupted. They have applied their new technique to two super-eruption sites and a pair of very large eruptions and found that it took them no more than 500 years to move from formation to eruption.
These results are described in the article "Melt inclusion shapes: Timekeepers of short-lived giant magma bodies" appearing in the November issue of the journal Geology.
"Geologists have developed a number of different 'timekeepers' for volcanic deposits. The fact that these techniques measure different processes and have different resolutions, has contributed to this lack of consensus. Our new method indicates that the process can take place within historically relevant spans of time," said Guilherme Gualda, associate professor of earth and environmental sciences at Vanderbilt University, who directed the project. The method was developed as part of the doctoral thesis of Ayla Pamukcu, who is now a post-doctoral researcher at Brown and Princeton Universities.
"The hot spot under Yellowstone National Park has produced several super-eruptions in the past. The measurements that have been made indicate that this magma body doesn't currently have a high-enough percentage of melt to produce a super-eruption. But now we know that, when or if it does reach such a state, we will only have a few hundred years to prepare ourselves for the consequences," Gualda said.
The researchers' geospeedometer is based on millimeter-sized quartz crystals that grew within the magma bodies that produced these giant eruptions. Quartz crystals are typically found in magmas that have a high percentage of silica. This type of magma is very viscous and commonly produces extremely violent eruptions. Mount St. Helens was a recent example.
When the crystals form, they often capture small blobs of molten magma - known as blebs or melt inclusions. Blebs are initially round. While the crystal is floating in hot magma, diffusion causes them to gradually acquire the polygonal shape of the crystal void that they occupy. But this faceting process can be halted if eruption occurs before complete faceting is achieved.
Using advanced 3-D X-ray tomography, the researchers were able to measure the size and shape of the melt inclusions with exquisite precision. In cases where the inclusions had not become completely faceted, the researchers could determine how much time had elapsed since they were enclosed.
"Previous studies provided us with the data we needed to calculate the rate of the faceting process. We then used this rate, in combination with our shape measurements, to calculate how long the crystal existed in the magma before the eruption," said Pamukcu.
In addition, the researchers compared the results obtained with faceting with results obtained using other techniques. Crystallization may cause variations in concentration of certain elements. In quartz, the element titanium can vary sharply between different zones or layers within the crystal. Over time, however, the process of diffusion gradually smooths out these variations. This process also stops at the eruption, so the shallower the slope of titanium concentrations across these boundaries today, the longer the crystal spent in magmatic conditions.
The physics of this process is also well known, so the researchers could use these measurements to provide an independent estimate of how long a crystal spent floating around in the melt. They found that the duration times they derived from the titanium diffusion measurements agreed closely with those produced by the faceting method.
They applied their geospeedometer to four large eruptions:
"Our current method will also work on smaller volcanic systems, as long as they erupt magmas that contain quartz crystals," said Pamukcu. "We are also confident that we can adapt these techniques to work with other minerals, which will allow us to make similar timescale calculations for other types of magmas and volcanoes, like the low-silica basalts commonly erupted from Hawaiian volcanoes."
Florence Bégue and Darren Gravley at the University of Canterbury in New Zealand were co-authors of the study.
The work was supported by Department of Energy--Geosciences grant DE-FG02-94ER14466 and National Science Foundation grants EAPSI-1209584, EAR-1321806, EAR-1151337 and EAR-0948528.
David F Salisbury | EurekAlert!
Greenland ice flow likely to speed up: New data assert glaciers move over sediment, which gets more slippery as it gets wetter
17.08.2017 | Swansea University
Climate change: In their old age, trees still accumulate large quantities of carbon
17.08.2017 | Universität Hamburg
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
18.08.2017 | Life Sciences
18.08.2017 | Physics and Astronomy
18.08.2017 | Materials Sciences