For decades geologists have been puzzled by the mechanisms that give rise to the volcanoes formed in the Pacific Ocean called the “ring of fire.” Accounting for about 10 to 25 percent of all volcanoes on earth, these arc volcanoes are produced when one of the plates that make up Earth’s crust plunges beneath another plate in a process called subduction.

Understanding when, how and at what depth fluids and molten rock from subducting plates are released, giving rise to molten magma that forms volcanic eruptions and producing many of the world’s major deposits of important metals was paramount to scientists.

How this process works could assist greatly in helping to locate these sources. Thanks to fieldwork, experiments and computer modeling carried out by Professor of Geology Timothy Grove of the Department of Earth, Atmospheric and Planetary Sciences (EAPS), graduate student Christy Till, and three colleagues, the mystery has now been solved.

“The new findings will force a rewriting of textbooks and encyclopedias,” Grove said. “The conventional understanding has been that the depth to these descending slabs under arc volcanoes is always 100 kilometers, but recent analysis shows that in fact the depth can vary considerably, from around 60 km to more than 170 km, depending on a number of factors.”

Grove also said that the discovery of this variability in depths was what led his team to question why that is, and one key variable turned out to be the characteristics of a particular mineral called chlorite that forms in the earth’s mantle above the oceanic crust. Chlorite contains a large amount of water, and this water is released when the chlorite breaks down at specific combinations of temperature and pressure. Chlorite breakdown occurs at particular depths in the Earth’s mantle determined by the exact angle of the slab as it plunges downward. Understanding the process that produces arc volcanoes is important because, among other things, most of the world’s major deposits of such metals as silver, copper and molybdenum occur in these formations. Knowing exactly how they form could eventually lead to a better ability to locate such deposits. 

According to Christy Till, “the stability of this mineral is the key factor in our paper, because that’s what limits the melting process to such a narrow range of conditions. The speed at which the two plates are converging, the team found, has relatively little effect on the melting depth. By knowing that process, we can independently come up with a model for the thermal structure below these volcanoes, and why arc magmas come from these certain depths. Until this research, we were still missing that link in how arc volcanoes form.”

In addition to Grove and Till, the research was carried out by EAPS graduate student Einat Lev, Nilanjan Chatterjee, a principal research scientist in EAPS, and Etienne Medard, a former EAPS researcher who is now a professor at Clermont-Ferrand in France. The research was supported by a grant from the National Science Foundation (NSF). 

http://web.mit.edu/newsoffice/2009/volcanoes-0605.html

http://thefutureofthings.com/headline/7250/mit-team-solves-volcanic-mystery.html

 Accessed: June 6, 2009

Microorganisms (or parts of them) have long been known become airborne and travel great distances. A new study however, has recently yielded the first in-situ data on their participation in cloud ice processes.

A team led by Kerri Pratt, a Ph.D. student of atmospheric chemistry in the Department of Chemistry and Biochemistry at the University of California, San Diego (UCSD), sampled water droplet and ice crystal residues using an Ice in Clouds Experiment – Layer Clouds (ICE-L). The ICE-L experiment was the first aircraft-based deployment of the Aircraft Aerosol Time-of-flight Mass Spectrometer (A-ATOFMS) nicknamed “Shirley.”

This research was funded by the National Science Foundation (NSF) and the National Center for Atmospheric Research (NCAR).

In a situation that is being described as ‘the holy grail’ of climate change, Analysis of ice crystals was launched from a specially outfitted C-130 aircraft operated by the National Center for Atmospheric Research. A type of cloud known as a wave cloud over Wyoming in the Fall of 2007 revealed that they were made up almost entirely of either dust or biological particles such as bacteria, fungal spores and plant material.

“If we understand the sources of particles that nucleate clouds and their relative abundance, then we can determine the impact of these different sources on climate,” said Pratt. “The climate change science field has long derived many of its projections from computer simulations of climate phenomena.”

According to Anne-Marine Schmoltner of the NSF’s Division of Atmospheric Sciences, “By sampling clouds in real time from an aircraft, these investigators were able to get information about ice particles in clouds at an unprecedented level of detail. By determining the chemical composition of the very cores of individual ice particles, they discovered that both mineral dust, and, surprisingly, biological particles play a major role in the formation of clouds.”

Aerosols, ranging from dust, soot and sea salt to organic materials, some of which travel thousands of miles, form the skeletons of clouds. Water and ice in the atmosphere condense around these nuclei and grow leading to precipitation. The present challenge is for scientists to understand how clouds form, as they play a critical role by both cooling the atmosphere and affecting regional precipitation processes.

Their findings also suggest that biological particles that get swept up in dust storms help to induce the formation of cloud ice and that their region of origin makes a difference. For example, dust transported from Asia could be influencing precipitation in North America. Researchers hope to use the ICE-L data to design future studies focused on examining the role such particles play in triggering rain or snowfall.

http://www.physorg.com/news161787442.html

http://digg.com/environment/Scientists_Find_High_Flying_Microbes_The_Clouds_are_Alive 

Accessed: May 22, 2009