3-D Model Mimics Volcanic Explosions; Shows Events Taking Place Underground

A 3-D model of a volcanic explosion, based on the 1980 eruption of Mount St. Helens in Washington state, may enhance our understanding of how some volcanic explosions occur and help identify of blast zones for potentially dangerous locations, according to an international team of volcanologists.

This is a profile view of the simulation of the 1980 blast at Mount St. Helens.

Credit: Istituto Nazionale di Geofisica e Vulcanologia, Italy.

"We took on the modeling of enormously complicated pyroclastic density currents, notably the classic, notorious May 1980 lateral blast that destroyed 500 square kilometers of forested terrain at Mount St. Helens," said Barry Voight, professor emeritus of geology and geological engineering, Penn State.

Mount St. Helens erupted catastrophically on May 18, 1980, creating a low-angle lateral blast with an astonishing energy and particle content. The blast lasted less than five minutes, but caused severe damage over 230 square miles, killing 57 people and destroying 250 homes and 47 bridges. The damage was not caused by lava flows, but by a fast moving current of superheated gas that carried with it a heavy load of debris.

"Volcanic lateral blasts are among the most spectacular and devastating of natural phenomena, but their dynamics are still poorly understood," the researchers reported in the current issue of the journal Geology.

This is a simulation of the May 18, 1980 blast at Mount St. Helens (USA) at 380 seconds.

Credit: Istituto Nazionale di Geofisica e Vulcanologia, Italy.

The researchers created the 3-D model using the parameters of the Mount St. Helens blast including equations to determine mass, momentum and the heat energy of the gas, along with the size, density, specific heat and thermal conductivity of the solid particles.

"We integrated a wide range of geophysical and geochemical data to develop rigorous initial and boundary conditions for hydrodynamics calculations that reproduced, to an amazing degree, the observed dynamics of the blast envelope," said Voight.

The 3-D model reproduced the Mount St. Helens blast, closely matching the complicated boundaries of the region of devastation and observed results on the ground. In the model, the areas of ground where pressures imply that trees would be blown down fit the actual locations of destroyed forests.

This is a simulation of the eruption of Mount St. Helens in 1980, birds eye view.

Credit: Istituto Nazionale di Geofisica e Vulcanologia, Italy.
"The calculations provided much insight into internal dynamics of the blast explosion cloud that could not be observed directly," said Voight.

According to the researchers, the most important factors controlling where the blast travels and causes damage are a combination of gravity and the shape of the terrain. Pyroclastic blasts are blocked by mountains and channeled down river ravines and canyons.

Previous models of the Mount St. Helens blast considered it to be dominated by a supersonic expanding jet of gas that originated at the volcanic vent. However, the research team suggests that apart from an initial burst that impacted a region less than 3.6 miles from the vent, the blast current was gravity driven.

The researchers found that as the distance from the vent increased, the blast current weakened because of the energy lost while trying to go over obstacles. They also show spreading in all directions caused a slowing of the flow and that particle sedimentation removed energy from the flow.

"Our present results demonstrate that, where detailed geological constraints are available and thanks to the availability of modern supercomputers, 3-D transient and multiphase flow models can fairly accurately reproduce the main large-scale features of blast scenarios," said Voight.

The researchers note that "such an improvement in our modeling capability will make it possible to more effectively map potential blast flows at blast-dangerous volcanoes worldwide."

Other researchers on the team are Tomaso Esposti Ongaro and Augusto Neri, Istituto Nazionale di Geofisica e Vulcanologia, Pisa, Italy; C. Widiwidjayanti, formerly at Penn State but now at Nanyang Technological University, Singapore; and Amanda B. Clarke, Arizona State University.

The National Science Foundation and the European Commission supported this research. Researchers at the U.S. Voight began work at Mount St. Helens in 1980 as a researcher at the Geological Survey Cascade Volcano Observatory.

 Contacts and sources:

A'ndrea Elyse Messer
Penn State

Algal Turf Scrubbers Clean Water With Sunlight

Byproducts useful for fertilizer, fuel and nutraceuticals could tip the economic balance in favor of the novel purification systems

An article published in the June issue of BioScience describes the early scale-up stage of a new biotechnology with environmental benefits and possible commercial potential. Algal turf scrubbers are field-sized, water-treatment systems that can extract excess nutrients from streams, canals, and lakes polluted by agricultural, domestic, and some industrial runoff.

They use sunlight as their principal source of energy and simultaneously restore oxygen levels. The devices work by pulsing contaminated water across algae that are allowed to grow on screens. Algal turf scrubbers produce waste suitable for use as a nitrogen- and phosphorus-rich fertilizer and for conversion to biofuel or high-value nutraceuticals. Some algal turf scrubbers can even operate in open water, thus minimizing loss of agricultural land to the systems.

The BioScience article, by Walter H. Adey of the Smithsonian Institution, Patrick C. Kangas of the University of Maryland, and Walter Mulbry of the US Department of Agriculture, notes that the need to clean wastewater and various types of runoff contaminated with nitrogen and phosphorus is immediate in many places where natural waters are polluted. Furthermore, some ecologists are worried about global supplies of phosphorus for use in fertilizer, so the byproduct could become more valuable over time.

The article stresses that algal turf scrubbing is not likely to ever be profitable just as a way of making fuel. Although more productive than terrestrial crops, algae, like other potential sources of biofuel, are expensive to cultivate, harvest, process, and convert into useful amounts of energy. But algal turf scrubbing could become common if the economic value of nutrient removal can be applied to the cost of building and running the units. That might depend on public policy that imposes a predictable cost on pollution of natural waters. But the fuel, fertilizer, and nutraceutical byproducts from algal turf scrubbing can only help.

 Contacts and sources:

Tim Beardsley
American Institute of Biological Sciences

The full text of the article is available for free download at www.aibs.org/bioscience-press-releases/.

Lasers Used To Form 3-D Crystals Made Of Nanoparticles

University of Michigan physicists used the electric fields generated by intersecting laser beams to trap and manipulate thousands of microscopic plastic spheres, thereby creating 3-D arrays of optically induced crystals.

The technique could someday be used to analyze the structure of materials of biological interest, including bacteria, viruses and proteins, said U-M physicist Georg Raithel.

Raithel is co-author of a research paper on the topic published online May 31 in the journal Physical Review E. The other author is U-M research fellow Betty Slama-Eliau.

The standard method used to characterize biological molecules like proteins involves crystallizing them, then analyzing their structure by bombarding the crystals with X-rays, a technique called X-ray crystallography. But the method cannot be used on many of the proteins of highest interest—such as cell-membrane proteins—because there's no way to crystallize those molecules.

"So we came up with this idea that one could use, instead of a conventional crystal, an optically induced crystal in order to get the crystallization of a sample that could be suitable for structural analysis," said Raithel, professor of physics and associate chair of the department.

To move toward that goal, Raithel and his colleagues are developing the laser technique using microscopically small plastic spheres instead of the molecules. Other researchers have created 3-D optically induced crystals, but Raithel said the crystals his team created are denser than those previously achieved.

The process involves shining laser beams through two opposed microscope lenses, one directly beneath the other. Two infrared laser beams are directed through each lens, and they meet at a common focal point on a microscope slide that holds thousands of plastic nanoparticles suspended in a drop of water.

The intersecting laser beams create electric fields that vary in strength in a regular pattern that forms a 3-D grid called an optical lattice. The nanoparticles get sucked into regions of high electric-field strength, and thousands of them align to form optically induced crystals. The crystals are spherical in shape and about 5 microns in diameter. A micron is one millionth of a meter.

Imagine an egg crate containing hundreds of eggs. The cardboard structure of the crate is the optical lattice, and each of the eggs represents one of the nanoparticles. Stack several crates on top of each other and you get a 3-D crystal structure.

"The crate is the equivalent of the optical lattice that the laser beams make," Raithel said. "The structure of the crystal is determined by the egg carton, not by the eggs."

The optical crystals dissipate as soon as the laser is switched off.

The research was funded by the National Science Foundation.

 Contacts and sources:

Jim Erickson
University of Michigan