History Of Quaternary Volcanism And Lava Dams In Western Grand Canyon

Daily Science Journal (Feb. 11, 2008) — John Wesley Powell wrote in 1895: “...what a conflict of water and fire there must have been [in western Grand Canyon]! Just imagine a river of molten rock running down over a river of melted snow.”

Toroweap Point in Grand Canyon national park. (Credit: iStockphoto/Natalia Bratslavsky)

Over 110 years later, a synthesis of new and existing dates on these lava flows shows that many are significantly younger than initially thought and all are less than 725 thousand years old. The geochronology data indicates four major episodes when lava flows either erupted into the canyon or flowed over the rim into it: 725-475 thousand years ago (ka), 400-275 ka, 225-150 ka, and 150-75 ka.

These flows formed lava dams in western Grand Canyon that had dramatic impact on the Colorado River.

This paper* presents light detection and ranging (lidar) data to establish the elevations of the tops and bottoms of basalt flow remnants along the river corridor. These data show the original extent of now-dissected intra-canyon flows and aid in correlation of flow remnants.

From 725 to 475 ka, volcanism built a high edifice within Grand Canyon in the area of the Toroweap fault, with dike-cored cinder cones on both rims and within the canyon itself. These large-volume eruptions helped drive the far-traveled basalt flows which flowed down-canyon over 120 km. A second episode of volcanism, from 400 to 275 ka, built a 215-m-high dam along the Hurricane fault, about 15 km downstream.

The ca. 200 and 100 ka flows (previously mapped as Gray Ledge) were smaller flows and lava cascades that entered the canyon from the north rim between the Toroweap and Hurricane faults.

The combined results suggest a new model for the spatial and temporal distribution of volcanism in Grand Canyon in which composite lava dams and edifices were generally leaky in proximal areas.

Available data suggest that the demise of volcanic edifices may have involved either large outburst-flood events or normal fluvial deposition at times when the river was established on top of basalt flows. These data highlight complex interactions of volcanism and fluvial processes in this classic locality.

This research, authored by Ryan Crow (University of New Mexico) et al. was published in the February issue of Geosphere, published by the Geological Society of America.

Adapted from materials provided by Geological Society of America.

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Magma And Volcanoes: Physicists Explain Dance Marathon Of Wispy Feature In Roiling Fluids

Daily Science Journal (Feb. 7, 2008) — Theoretical physicists at the University of Chicago are suggesting how thin spouts of magma in the Earth's mantle can persist long enough to form hotspot volcanism of the type that might have created the Hawaiian Islands.

University of Chicago physicists Wendy Zhang (left) and Laura Schmidt explain a feature of convecting fluids that colleagues have observed in laboratory experiments. The feature may help explain how hotspot volcanism created the Hawaiian Islands and other such landforms. (Credit: Dan Dry)

Their calculations also apply to tendrils only a few inches long that form in convecting fluids under laboratory conditions. University of Chicago graduate student Laura Schmidt and Wendy Zhang, an Assistant Professor in Physics, will detail their findings in the Feb. 1 issue of the journal Physical Review Letters.

The work was inspired by laboratory experiments conducted by Anne Davaille in France that mimic, in a simplified way, convecting bubbles of magma as they might look deep beneath the Earth's surface. "This is one robust feature of thermal convection," Zhang said.

"It's a useful thing to know because it's the kind of thing that happens in all sorts of different industries, in all sorts of different contexts." These include oil extraction, the chemical industry and in certain biotechnological applications.

Earth scientists also have theorized that mantle plumes form on a regional scale in the Earth's interior, sometimes breaking the surface to form small landmasses, including Hawaii and Iceland. Nevertheless, debate swirls around how, or even if, mantle plumes can account for such surface features.

Geophysicists often liken a pot of boiling water as a smaller, more rapid version of the convection that takes place in the mantle, the layer of Earth that lies between the surface crust and its core. But unlike a pot of water, the Earth's interior consists of layers with different properties.

In laboratory experiments, Anne Davaille, a geophysicist at the University of Paris 7, studies convection in a small tank by heating two layers of colored liquids of differing densities. She observed the formation and persistence of thin tendrils between the layers, which correspond to subsurface plumes measuring scores of miles across.

"It seems so thin and tenuous, how could it possibly manage to hold itself in place over time as everything else is going on around it?" Zhang asked. "Somehow, they manage to hold themselves together."

The tendrils persist for hours, even as experimental conditions change. "These tendrils have fluid flowing through them, and it starts to mix the two layers," Schmidt said. "When the two layers mix, then the viscosity of the layers changes as well."

Following a series of visits to Davaille's lab, Schmidt and Zhang sought to mathematically explain the phenomenon.

"When you look at the shape of these very thin tendrils, there's something very striking that Anne noticed right away," Zhang said. The tendrils seem to emerge from flow lines that resemble the flared-out end of a trumpet. This trumpet shape marked the location of a stagnation point. Both Davaille's experiments and Schmidt's calculations agree: The thinnest tendrils that persist have a stagnation point.

Schmidt had seen a similar stagnation point in experiments she conducted in the laboratory of Sidney Nagel, the Stein-Freiler Distinguished Service Professor in Physics at the University of Chicago. Those experiments involved unmixable fluids, such as water and oil, instead of the fresh water and salt water mixing in Davaille's laboratory.

Nevertheless, the experimental similarities provided Schmidt and Zhang insights that helped solve the problem. In previous studies, other theoreticians suggested how large flows might rise through the tendrils from the base of the hot spots, Schmidt said. She and Zhang approached the problem differently.

"We include the effect of the stagnation point," Schmidt explained. "Our tendrils are really a thin skin or thin layer of the surface between the fluids that is drawn up. It's not a bulk flow going up through the tendril."

Adapted from materials provided by University of Chicago, via EurekAlert!, a service of AAAS.

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Double Star TC-1 Completes Its Mission ; Details Of Solar Particles Penetrating The Earth's Environment Revealed

Daily Science Journal (Oct. 19, 2007) — TC-1, one of the two satellites of the CNSA/ESA Double Star mission, was decommissioned on 14 October as its designed orbit lifetime came to an end. The satellite re-entered Earth’s atmosphere and turned to dust during its descent.

Flying in formation around the Earth, they relay detailed information about how solar wind affects our planet in 3D. The satellites are called Rumba, Salsa, Samba and Tango. (Credit: ESA)

Along with its twin TC-2, TC-1 is the first satellite built and operated by the Chinese National Space Administration (CNSA) in cooperation with ESA. Along with its twin and the four Cluster satellites, TC-1 has helped accomplish much during its lifetime.

The four years during which Double Star was operational brought in new perspectives concerning the boundaries of the magnetosphere and the fundamental processes that are playing a role in the transport of mass, momentum and energy into the magnetosphere. Thanks to the measurements of TC-1, there was a chance to observe the evolution of structures and physical processes at small scales with Cluster, and then on large scales with Double Star.

Here we list some of the most interesting results where TC-1 played a crucial role.

Space is fizzy

Above our heads, at the bow shock, where the Earth’s magnetic field meets the constant stream of gas from the Sun, thousands of bubbles of superheated gas, or ion density holes, are constantly growing and popping. These bubbles were discovered by Cluster and Double Star together, and the discovery allowed scientists to better understand the interaction between the solar wind and the Earth’s magnetic field.

Celestial chorus further away

Chorus emissions are waves naturally generated in space close to the magnetic equator. They play an important role in creating killer electrons that can damage solar panels and electronic equipments of satellites and are a hazard for astronauts. It was found that these waves are created further away from Earth during high geomagnetic activity. This information is crucial to be able to forecast their impact.

Oscillations of Earth’s natural cloak of magnetism

The four Cluster satellites and TC-1 unexpectedly found themselves engulfed by waves of electrical and magnetic energy as they travelled through Earth’s night-time shadow. Something had set the tail of Earth’s natural cloak of magnetism oscillating, like waves created by a boat travelling across a lake. The data collected gave scientists an important clue to the effects of space weather on Earth’s magnetic field.

"Double Star has demonstrated mutual benefit and fostered scientific cooperation in space research between China and Europe. But there is still much more to come as the full, high-resolution data archive becomes available," says Philippe Escoubet, ESA’s Cluster and Double Star Project Scientist.

Adapted from materials provided by European Space Agency.

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Details Of Solar Particles Penetrating The Earth's Environment Revealed

Co-ordinated efforts by China/ESA’s Double Star and ESA’s Cluster spacecraft have allowed scientists to zero in on an area where energetic particles from the Sun are blasting their way through the Earth’s magnetic shield. Solar material penetrating the Earth's magnetic shield can represent a hazard to both astronauts and satellites.

This sketch shows the orbits of the Cluster and Double Star (TC-1) spacecraft on 8 May 2004, when the five satellites observed magnetic channels created by the merging of the Sun and the Earth's magnetic fields. Such events, called 'Flux Transfer Events,' allow solar particles to break through the Earth's magnetic shield and penetrate the Earth's environment. (Image courtesy of European Space Agency)

On 8 May 2004, one of the two Double Star satellites (TC-1) and all four Cluster spacecraft found themselves in the firing line. For about 6 hours, the Cluster spacecraft were buffeted every 8 minutes by intense flows of electrically charged particles released by the Sun. The Double Star TC-1 spacecraft had it even rougher, being blasted every four minutes for eight hours.

During such events, magnetic channels created by the merging of the Sun and the Earth’s magnetic fields allow solar particles to break through the Earth’s magnetic shield and penetrate the Earth’s environment. Physicists call the occurrence of these magnetic channels Flux Transfer Events. Each magnetic channel appears like a curve shaped tube that can be anything from 5000 to 25000 kilometres in diameter. One end of the magnetic flux tube is connected to Earth while the other end is connected to the solar wind.

The basic physical mechanism responsible for the occurrence of flux transfer events is called magnetic reconnection. In the 1950s, space physicists believed that magnetic reconnection let solar particles break through at a steady rate. That view changed in the late 1970s, when several studies showed that the magnetic reconnection could also be intermittent and take place in pulses, lasting a few minutes. Each pulse produces a magnetic flux tube (a Flux Transfer Event).

On 8 May 2004, these magnetic flux tubes swept over Cluster and Double Star again and again. As the Cluster and Double Star data clearly showed, the same location underwent magnetic reconnection several times, creating new successive magnetic flux tubes to channel more charged particles towards the Earth. The observations stopped probably because the spacecraft moved out of range and not because the reconnection region weakened in any way.

The data from the five spacecraft allowed scientists led by Aurélie Marchaudon of the Laboratoire de Physique et Chimie de l’Environnement, Centre Nationale de la Recherche Scientifique (CNRS) and Université d’Orléans, Orléans, France to triangulate the location of the magnetic reconnection region, and to deduce its size. They found that the reconnection site was located on the daylight west side of the Earth’s magnetic shield and was around 25000 kilometres across. A computer simulation of the event, conducted by Jean Berchem of the University of California Los Angeles (UCLA) and his team, confirmed the possibility of magnetic reconnection occurring at that location.

Although intermittent reconnection has been observed in the past, this was one of the longest series of continuous observations ever taken of a magnetic reconnection region in the Earth’s magnetosphere. Perhaps most surprising is that 8 May 2004 was just relatively a normal day for the Earth’s magnetic field. There were no large magnetic storms on Earth, or spectacular aurorae to fill the night sky. However, Cluster and Double Star revealed that energetic particles from the Sun were blasting their way through the Earth’s magnetic shield and penetrating the Earth’s environment.

Each day, Cluster and Double Star return more observations that allow scientist to understand the invisible magnetic turbulence high above our heads.

Adapted from materials provided by European Space Agency.

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