Research News: Helium Isotopes Point to New Sources of Geothermal Energy





Arizona State geochemist Matthijs van Soest samples surface water in the northern Basin and Range. The sample is collected without direct exposure to air and stored in the copper tube, foreground left, which will be sealed by crimping.
Arizona State geochemist Matthijs van Soest samples surface water in the northern Basin and Range. The sample is collected without direct exposure to air and stored in the copper tube, foreground left, which will be sealed by crimping.

In a survey of the northern Basin and Range province of the western United States, geochemists Mack Kennedy of the Department of Energy’s Lawrence Berkeley National Laboratory and Matthijs van Soest of Arizona State University have discovered a new tool for identifying potential geothermal energy resources.



Currently, most developed geothermal energy comes from regions of volcanic activity, such as The Geysers in Northern California. The potential resources identified by Kennedy and van Soest arise not from volcanism but from the flow of surface fluids through deep fractures that penetrate the earth’s lower crust, in regions far from current or recent volcanic activity. The researchers report their findings in the November 30, 2007 issue of Science.



“A good geothermal energy source has three basic requirements: a high thermal gradient – which means accessible hot rock – plus a rechargeable reservoir fluid, usually water, and finally, deep permeable pathways for the fluid to circulate through the hot rock,” says Kennedy, a staff scientist in Berkeley Lab’s Earth Sciences Division. “We believe we have found a way to map and quantify zones of permeability deep in the lower crust that result not from volcanic activity but from tectonic activity, the movement of pieces of the Earth’s crust.”



Kennedy and van Soest made their discovery by comparing the ratios of helium isotopes in samples gathered from wells, surface springs, and vents across the northern Basin and Range. Helium-three, whose nucleus has just one neutron, is made only in stars, and Earth’s mantle retains a high proportion of primordial helium-three (compared to the minuscule amount found in air) left over from the formation of the solar system. Earth’s crust, on the other hand, is rich in radioactive elements like uranium and thorium that decay by emitting alpha particles, which are helium-four nuclei. Thus a high ratio of helium-three to helium-four in a fluid sample indicates that much of the fluid came from the mantle.



High helium ratios are common in active volcanic regions, where mantle fluids intrude through the ductile boundary of the lower crust. But when Kennedy and van Soest found high ratios in places far from volcanism, they knew that mantle fluids must be penetrating the ductile boundary by other means.



The geology of the region was the clue. The Basin and Range is characterized by mountain ranges that mostly run north and south, separated by broad, relatively flat-floored valleys (basins), which are blocks of crust that have sunk and become filled with sediment eroded from the uplifted mountains. The alternating basin and range topography is the result of crustal spreading by east to west extension, which has occurred over the past approximately 30 million years. The Earth’s crust in the Basin and Range is some of the thinnest in the world, resulting in unusually high thermal gradients.


The faces of mountain blocks in the Basin and Range clearly exhibit the normal faults that result as the blocks are pulled apart by the extension of the crust. Normal faults form high-angle pathways deep down into the brittle upper crust. But as the fault plane approaches the ductile lower crust, changes in the density and viscosity of the rock refract the principle stress acting on the fault, deflecting the fault plane, which becomes more horizontal. It is from these deep, horizontally-trending faults that Kennedy thinks permeable passageways may emanate, penetrating the ductile boundary into the mantle.



One of the most seismically active areas in the Basin and Range occurs in what is called the central Nevada seismic belt. The researchers’ detailed studies in this area, notably at the Dixie Valley thermal system next to the Stillwater range, established that the highest helium ratios were restricted to fluids emerging from the Stillwater range-front fault system.



The northern Basin and Range, which Kennedy and van Soest surveyed on behalf of DOE’s Office of Basic Energy Sciences and Office of Geothermal Technologies, includes parts of California, Nevada, Oregon, Idaho, and Utah. In their survey the researchers mapped the steady progression from low helium ratios in the east to high ratios in the west. The distribution of the increasing ratios corresponds remarkably with an increase in the rate and a change in the direction of crustal extension, which shifts from an east to west trend across the Basin and Range to a northwest trend.



This change in rate and direction reflects the added shear strain induced by the northward movement of the Pacific Plate past the North American Plate. Kennedy and van Soest believe that the added component of shear strain and increasing extension rate tear open fluid pathways through the ductile lower crust, into the mantle. The high helium isotope ratios they found, indicating potential new sources of geothermal energy, were superimposed upon the general background trend: anomalously high ratios map zones of higher than average permeability.



“We have never seen such a clear correlation of surface geochemical signals with tectonic activity, nor have we ever been able to quantify deep permeability from surface measurements of any kind,” says Kennedy. The samples they collected on the surface gave the researchers a window into the structure of the rocks far below, with no need to drill.



With the urgent need to find energy sources that are renewable and don’t emit greenhouse gases, geothermal energy is ideal – “the best renewable energy source besides the sun,” Kennedy says. Accessible geothermal energy in the United States, excluding Alaska and Hawaii, has been estimated at 9 x 1016 (90 quadrillion) kilowatt-hours, 3,000 times more than the country’s total annual energy consumption. Determining helium ratios from surface measurements is a practical way to locate some of the most promising new resources.



“Flow of Mantle Fluids Through the Ductile Lower Crust: Helium Isotope Trends,” by B. Mack Kennedy and Matthijs C. van Soest, appears in the 30 November 2007 issue of Science and is available to subscribers at http://dx.doi.org/10.1126/science.1147537.

Findings may reveal secret to interaction between Earth’s core and mantle





The boundaries between grains of rock could be a pathway for metals to move between Earth's core and mantle. - Photo Credit: Leslie Hayden/Rensselaer Polytechnic Institute
The boundaries between grains of rock could be a pathway for metals to move between Earth’s core and mantle. – Photo Credit: Leslie Hayden/Rensselaer Polytechnic Institute

Leslie Hayden’s research into deep Earth interactions has led to some important findings, particularly for someone so new to the field, and the scientific world is paying attention. Hayden, a graduate student at Rensselaer Polytechnic Institute, is first author on a paper to be published in the scientific journal Nature. The findings will be published in the Nov 29, 2007 edition of the journal.



Hayden performed her research under the guidance of Bruce Watson, Institute Professor of Science at Rensselaer.



Hayden used some powerful equipment and creative techniques to uncover a potential pathway for metals to move between the core and mantle of the Earth. “Core-mantle interactions are a hotly debated topic,” Hayden said. “Some scientists believe that there is no chemical interaction at all between the Earth’s molten metal core and solid silicate mantle. Others believe they see signs of such interaction, but no mechanism or pathway has been found that could deliver metal atoms over distances of more than a few meters. ”



Hayden’s experiments may have uncovered such a pathway. If true, the findings could have broad implications on how geologists understand the deep Earth. They could also one day provide important information on how valuable elemental resources like gold and platinum are deposited.


Hayden and Watson developed an experiment that simulated the interface between the core of the Earth and the mantle. The highly pressurized core consists mostly of iron and nickel and is also believed to contain other “iron-loving” elements like gold and platinum. The mantle is comprised of silicate rocks rich in magnesium. For the experiments they placed a rock that is representative of the material found in the Earth’s mantle in between what they refer to as a source and a sink layer. The source layer was one of the metals found in the core, such as gold, platinum, copper, and other lesser known metals like ruthenium and tungsten. For each metal, the miniaturized core/mantle boundary was then heated to extreme temperatures and pressures to represent conditions in the deep Earth. Following the experiments, each source metal was found in the sink, proving that the metals could in fact find a pathway through the mantle rock that is believed to be impenetrable by some scientists.



Hayden and Watson hypothesize that the metal atoms move along the surfaces formed between adjacent grains of the mantle rock. Like a sugar cube, mantle rocks are comprised of individual crystals squeezed tightly together into a larger structure. The atoms of the core metals are too large to diffuse through the structured arrangement of atoms that make up an individual crystal or grain of rock. But, the boundary between each grain is less crowded with atoms, according to the researchers, and could be a fast pathway for metals to migrate between the mantle and core.



“[In our experiments], some of the metals moved through grain boundaries at surprisingly fast rates – about as fast as sodium ions move through water,” Hayden said. “This shows that metals can in fact travel over great distances through mantle materials. Over geologic time, this diffusion of metals could have a significant impact on their distribution in the Earth.” Their experiments revealed that some elements could move up to 100 kilometers through the Earth’s mantle in a billion years.



The findings have implications for the field, but also for broader economic reasons, Hayden explains. If these metals are able to move out of core and into the mantle as their findings suggest, they would enter the geologic upwelling of mantle convection and could be gradually moved toward Earth’s surface, potentially leading to valuable deposits. “As we learn more about the movement of precious and base metals through the Earth, we could at some point find out how they are deposited, where, and why,” she said.



The research was funded by the National Science Foundation (NSF).



Hayden is from Marlton, New Jersey. She plans to become a post-doctoral researcher at UCLA upon completion of her doctorate at Rensselaer, expected in December.

Rising tides intensify non-volcanic tremor in Earth’s crust


For more than a decade geoscientists have detected what amount to ultra-slow-motion earthquakes under Western Washington and British Columbia on a regular basis, about every 14 months. Such episodic tremor-and-slip events typically last two to three weeks and can release as much energy as a large earthquake, though they are not felt and cause no damage.



Now University of Washington researchers have found evidence that these slow-slip events are actually affected by the rise and fall of ocean tides.



“There has been some previous evidence of the tidal effect, but the detail is not as great as what we have found,” said Justin Rubinstein, a UW postdoctoral researcher in Earth and space sciences.



And while previous research turned up suggestions of a tidal pulse at 12.4 hours, this is the first time that a second pulse, somewhat more difficult to identify, emerged in the evidence at intervals of 24 to 25 hours, he said.



Rubinstein is lead author of a paper that provides details of the findings, published Nov. 22 in Science Express, the online edition of the journal Science. Co-authors are Mario La Rocca of the Istituto Nazionale di Geofisica e Vulcanologia in Italy, and John Vidale, Kenneth Creager and Aaron Wech of the UW.



The most recent tremor-and-slip events in Washington and British Columbia took place in July 2004, September 2005 and January 2007. Before each, researchers deployed seismic arrays, each containing five to 11 separate seismic monitoring stations, to collect more accurate information about the location and nature of the tremors. Four of the arrays were placed on the Olympic Peninsula in Washington and the fifth was on Vancouver Island in British Columbia.


The arrays recorded clear twice-a-day pulsing in the 2004 and 2007 episodes, and similar pulsing occurred in 2005 but was not as clearly identified. The likely source from tidal stresses, the researchers said, would be roughly once- and twice-a-day pulses from the gravitational influence of the sun and moon. The clearest tidal pulse at 12.4 hours coincided with a peak in lunar forcing, while the pulse at 24 to 25 hours was linked to peaks in both lunar and solar influences.



The rising tide appeared to increase the tremor by a factor of 30 percent, though the Earth distortion still was so small that it was undetectable without instruments, said Vidale, a UW professor of Earth and space sciences and director of the Pacific Northwest Seismograph Network.



“We expected that the added water of a rising tide would clamp down on the tremor, but it seems to have had the opposite effect. It’s fair to say that we don’t understand it,” Vidale said.



“Earthquakes don’t behave this way,” he added. “Most don’t care whether the tide is high or low.”



The researchers were careful to rule out noise that might have come from human activity. For instance, one of the arrays was near a logging camp and another was near a mine.



“It’s pretty impressive how strong a signal those activities can create,” Rubinstein said, adding that the slow-slip pulses were recorded when those human activities were at a minimum.



The work was funded by the National Science Foundation, and instruments were provided by the Incorporated Research Institutions for Seismology, Istituto Nazionale di Geofisica e Vulcanologia and Earthscope.

Dunes, climate models don’t match up with paleomagnetic records





Sandstone cliff in Vermillion Cliffs National Monument, Ariz., composed of the deposits of about 15 large, Jurassic sand dunes (person for scale in upper right). Each dune migrated toward the present southeast (toward the left in this photo). The dune sand accumulated about 200 million years ago, just above sea level in a slowly subsiding sedimentary basin. Circulating groundwater cemented the sand into sandstone. Uplift of the region in the last 10 million years led to erosion of the rocks, forming canyons and cliffs. Climate models constructed for the supercontinent Pangaea suggest that the sands accumulated near the equator, and were swept by strong monsoonal winds that reversed direction every six months. Evidence based on the magnetic properties of rocks; however, indicate that the sand accumulated much farther north -- about 20 degrees north of the equator. (Image copyright Science)
Sandstone cliff in Vermillion Cliffs National Monument, Ariz., composed of the deposits of about 15 large, Jurassic sand dunes (person for scale in upper right). Each dune migrated toward the present southeast (toward the left in this photo). The dune sand accumulated about 200 million years ago, just above sea level in a slowly subsiding sedimentary basin. Circulating groundwater cemented the sand into sandstone. Uplift of the region in the last 10 million years led to erosion of the rocks, forming canyons and cliffs. Climate models constructed for the supercontinent Pangaea suggest that the sands accumulated near the equator, and were swept by strong monsoonal winds that reversed direction every six months. Evidence based on the magnetic properties of rocks; however, indicate that the sand accumulated much farther north — about 20 degrees north of the equator. (Image copyright Science)

For a quarter-century or more, the prevailing view among geoscientists has been that the portion of the ancient supercontinent of Pangea that is now the Colorado Plateau in southern Utah shifted more than 1,300 miles north during a 100-million year span that ended about 200 million years ago in the early Jurassic Period, when Pangea began to break up.



Paleomagnetic records are found in iron-bearing minerals in rocks and can record the direction of the Earth’s magnetic field at the time of their formation. Paleomagnetism is an important tool for geoscientists in tracking the movement of Earth’s tectonic plates over time and records in North America indicate that the Colorado Plateau moved from the equator to about 20 degrees north latitude from 300 million years ago to 200 million years ago.



But new research by geoscientists from the University of Nebraska-Lincoln and the University of Michigan challenges that theory, based on extensive climate modeling studies and sedimentary records found from Wyoming into Utah and Arizona.



In the Nov. 23 issue of the journal Science, UNL geoscientists Clinton Rowe, David Loope and Robert Oglesby, former UNL graduate student Charles Broadwater, and Rob Van der Voo of the University of Michigan, report findings that indicate the area must have remained at the equator during the time in question.



“It’s a puzzle, a ‘conundrum’ is the word we like to use,” Oglesby said. “And in the Science paper, we’re not solving the conundrum, we’re raising the conundrum.”



The root of the conundrum is Loope’s ongoing research in the Colorado Plateau that began when he was working on his doctorate at the University of Wyoming in the early 1980s. A sedimentologist and an expert on dune formation, he eventually saw that from central Wyoming into central Utah, ancient dunes preserved in the region’s 200 million- to 300-hundred-million-year-old sandstone formations all faced southwest, meaning that the winds over that extensive area were almost constantly from the northeast. As his study progressed, he discovered that the direction of the dunes shifted to the southeast in what is now southern Utah, meaning the wind direction shifted to the northwest. What’s more, those prevailing winds were consistent over the entire 100 million years in question and the shift in wind direction could only have occurred at the equator.



“I thought that was very curious,” Loope said. “It didn’t seem to fit with what we think we know about where the continents were.”



Loope is also a paleoclimatologist (someone who studies ancient climates), as are Rowe and Oglesby, who also have expertise in climate modeling. The three geoscientists began working together, trying to find a computerized climate model that would explain the discrepancy, but they couldn’t find any that worked.





Jurassic Navajo Sandstone in Zion National Park, southern Utah. The sloping lines within the sandstone (crossbeds) indicate the sediment accumulated in a large dune field. (Image copyright Science)
Jurassic Navajo Sandstone in Zion National Park, southern Utah. The sloping lines within the sandstone (crossbeds) indicate the sediment accumulated in a large dune field. (Image copyright Science)

“We ran the model in any different number of configurations just to see if we could make it do something different,” Rowe said. “It didn’t matter what we did to it, as long as you had some land, and it was distributed north and south of the equator, you would end up with this monsoonal flow that matched these records from the dunes.



“The equator is the only place you could get this large-scale arc of winds that turn from the northeast to the northwest as they moved south. Nowhere else would you get that as part of the general circulation unless the physics of the world 200 million years ago was very different from what it is today. And we just don’t think that’s the case.”



Puzzled by the discrepancy between their research and the paleomagnetic records, they turned to Van der Voo, an expert on paleomagnetism.



“We brought Rob in to try to see if he could help us sort it out, and he’s like, ‘Gosh, guys, I don’t know. This is a conundrum,'” Oglesby said. “It’s important to note that we have not just a paleomag person as a co-author, but arguably the best-known paleomag person in the world — and he’s as confused as we are.”



Van der Voo agreed that, for now, there’s no clear answer to the conundrum.



“The nicest thing would have been if we had a solution, but we don’t,” Van der Voo said. “All we can say is that we have this enigma, so perhaps our model of Pangea for the period in question is wrong or the wind direction didn’t follow the common patterns that we recognize in the modern world. Neither seems likely, but we’re bringing this inconsistency to the attention of the scientific community in hopes of stimulating further research.”



And further research is exactly what’s on the agenda, Oglesby said.



“We’ll come up with everything we can possibly think of,” he said. “From the point of view of the climate model, the paleogeography, the vegetation, the topography, local-scale vs. large-scale, paleomag, going back and rethinking everything that the dunes tell us. We’ll go back to square one in everything, trying to figure it out.”

Giant submarine landslide identified





Bathymetric image showing the ocean floor off the northwest coast of Africa. - Photo Courtesy of T. Le Bas
Bathymetric image showing the ocean floor off the northwest coast of Africa. – Photo Courtesy of T. Le Bas

An enormous submarine landslide that disintegrated 60,000 years ago produced the longest flow of sand and mud yet documented on Earth. The massive submarine flow travelled 1,500 kilometres – the distance from London to Rome – before depositing its load.



Details of the landslide and consequent sediment flow are reported online today in Nature by Dr Peter Talling from the University of Bristol, with colleagues from the National Oceanography Centre in Southampton and several other institutions.



Dr Talling said: “The volume of sediment transported by this flow in the deep ocean is difficult to comprehend. It was one of the largest movements of material ever to occur on our planet. This mass was ten times that transported to the ocean every year by all of the Earth’s rivers. The flow was sometimes over 150 km wide, spread across the open sea floor.”



Perhaps the most remarkable thing about this giant submarine flow is that it travelled hundreds of kilometres without depositing any sediment on the vast expanse of sea floor that it passed over.


Sediment deposition was finally triggered by a remarkably small but abrupt decrease in sea-floor gradient (from 0.05˚ to 0.01˚). For comparison, most premiership soccer pitches have a gradient of less than 1˚ to help their drainage.



Man is placing more and more structures on the sea floor, including installations for recovering subsurface oil and gas reserves that can be worth hundreds of millions of dollars. Understanding the cause and evolution of these infrequent undersea flows helps to assess any potential hazards posed to such structures.



Installations involved in oil and gas recovery are typically sited on slopes of greater than 0.05˚. Cores collected next to these installations to help design their foundations are often used for subsequent geohazard analysis.



This work suggests that a more accurate record of these flows is found by coring in the low-gradient basin plains which may be hundreds of kilometres from the installations.

Strange Alaska rivers flow through mountain range





Two rivers, the Delta and the Nenana, flow to the north of the Alaska Range despite having their headwaters south of the Alaska Range. - Drawing by Larry Gedney
Two rivers, the Delta and the Nenana, flow to the north of the Alaska Range despite having their headwaters south of the Alaska Range. – Drawing by Larry Gedney

Alaska’s landscape has an unusual feature that allows us to enjoy cheap bananas in Fairbanks and other things that make life better in the subarctic. The Nenana River, born on the south side of the Alaska Range, makes a U-turn and flows north through the mountains. With it comes a wide, low corridor that has favored construction of both the Alaska Railroad and the Parks Highway.



“Ordinarily, a mountain range is a pretty good barrier,” said Don Triplehorn, a man curious about many things and a professor emeritus at the University of Alaska Fairbanks. He recently described the curious behavior of the Nenana.



“It flows out to the south, downhill as any decent river should, but then it turns west and then north, past McKinley,” Triplehorn said “That’s really unusual.”



And the Nenana River isn¹t the only major waterway cutting through the Alaska Range. The Delta River does the same thing, originating south of the Alaska Range but then flowing north through the mountains.



“These are rivers that cut across one of the highest mountain ranges in the world,” Triplehorn said. ³The broad, low passes that come with them are convenient routes for highways, pipelines and microwave stations, as well as people, plants, and animals.”


Why do these two major rivers seem to defy logic by running through the Alaska Range? Triplehorn put forth a theory suggested by his friend and geologist Tom Hamilton of Anchorage that glacial ice flowing northward across the range scoured the broad, almost flat valleys through which the rivers flow.



The Alaska Range rose about 6 million years ago, Triplehorn said. During the last two million years or so, Earth went through a major ice age, and the Alaska Range south of Fairbanks looked something like the Greenland ice cap. Since moisture came from the south then as it often does now, the high point of the ice shifted southward. Ice could then flow away from the high point, and in a few instances it flowed northward, scouring valleys across the buried mountains. As the glaciers receded, meltwater streams that were to become the Nenana and Delta flowed northward down the valleys, maintaining their paths after the ice sheet disappeared.



There are differing theories of why the rivers cut through the Alaska Range, but textbook concepts on why rivers run through mountain ranges don¹t explain the courses of the Nenana and Delta rivers, Triplehorn said.



Whatever the reason for the Delta and the Nenana, life here would be different without them. Without the passes, Fairbanks probably wouldn’t exist, Triplehorn said, because human settlement north of the Alaska Range probably would have been on the Yukon River and its tributaries.



And, we need no tunnels to cross the Alaska Range, like the thousands who pass through Colorado’s Eisenhower Tunnel that accommodates interstate route 70 at 11,000 feet. Our expansive passes through the Alaska Range have for thousands of years allowed the easy movement of people, animals, oil, and trucks carrying bananas.



“It’s a good example of how geography and geology create history,” Triplehorn said.

‘Noah’s flood’ kick-started European farming


The flood believed to be behind the Noah’s Ark myth kick-started European agriculture, according to new research by the Universities of Exeter and Wollongong, Australia. Published in the journal Quaternary Science Reviews, the research paper assesses the impact of the collapse of the North American (Laurentide) Ice Sheet, 8000 years ago. The results indicate a catastrophic rise in global sea level led to the flooding of the Black Sea and drove dramatic social change across Europe. The research team argues that, in the face of rising sea levels driven by contemporary climate change, we can learn important lessons from the past.



The collapse of the Laurentide Ice Sheet released a deluge of water that increased global sea levels by up to 1.4 metres and caused the largest North Atlantic freshwater pulse of the last 100,000 years. Before this time, a ridge across the Bosporus Strait dammed the Mediterranean and kept the Black Sea as a freshwater lake. With the rise in sea level, the Bosporus Strait was breached, flooding the Black Sea. This event is now widely believed to be behind the various folk myths that led to the biblical Noah’s Ark story. Archaeological records show that around this time there was a sudden expansion of farming and pottery production across Europe, marking the end of the Mesolithic hunter-gatherer era and the start of the Neolithic. The link between rising sea levels and such massive social change has previously been unclear.


The researchers created reconstructions of the Mediterranean and Black Sea shoreline before and after the rise in sea levels. They estimated that nearly 73,000 square km of land was lost to the sea over a period of 34 years. Based on our knowledge of historical population levels, this could have led to the displacement of 145,000 people. Archaeological evidence shows that communities in southeast Europe were already practising early farming techniques and pottery production before the Flood. With the catastrophic rise in water levels it appears they moved west, taking their culture into areas inhabited by hunter-gatherer communities.



Professor Chris Turney of the University of Exeter’s School of Geography, Archaeology and Earth Resources, lead author of the paper, said: “People living in what is now southeast Europe must have felt as though the whole world had flooded. This could well have been the origin of the Noah’s Ark story. Entire coastal communities must have been displaced, forcing people to migrate in their thousands. As these agricultural communities moved west, they would have taken farming with them across Europe. It was a revolutionary time.”



The rise in global sea levels 8000 years ago is in-line with current estimates for the end of the 21st century. Professor Chris Turney continued: “This research shows how rising sea levels can cause massive social change. 8,000 years on, are we any better placed to deal with rising sea levels? The latest estimates suggest that by AD 2050, millions of people will be displaced each year by rising sea levels. For those people living in coastal communities, the omen isn’t good.”

Scientists reveal secrets of ancient ocean in new book





The Rheic Ocean separated two major land masses 430 million years ago. - art by: Christina Ullman, Ullman Design
The Rheic Ocean separated two major land masses 430 million years ago. – art by: Christina Ullman, Ullman Design

Call it the ocean that time forgot. About 400 million years ago, the Rheic Ocean played a big role in Earth’s history. When this massive body of water closed, the Appalachians were lifted to Himalayan heights and the planet’s continents slammed together to form the supercontinent of Pangaea. Dinosaurs and early mammals evolved to traverse the large swath of land, spreading life to every corner of the globe.



But the Rheic Ocean doesn’t get much attention in the field of geology today. In fact, American texts give usually credit to an older ancient sea, the Iapetus, for creating the Appalachians.



Ohio University geologist Damian Nance and colleagues now hope to set the record straight with a new book published this fall by the Geological Society of America. It pulls together recent data from a team of UNESCO-funded scientists in the United States, Germany, Britain, Portugal, Turkey and several former Eastern Block countries who have spent years combing for better geological evidence of this ancient ocean and its legacy.



The Rheic Ocean opened 480 million years ago and, by 430 million years ago, separated two major land masses. To the north was Laurentia, which comprised North America, Europe, Greenland and part of Asia. To the south lay Gondwana, which comprised Africa, South America, Antarctica, Australia and India.



The sea closed some 340 million years ago, which pushed the continents together and created two mountain ranges: the Appalachian mountains of North America and the Variscan Belt of Europe, which runs across southern Europe and North Africa from Ireland to the Czech Republic and from Morocco to the Black Sea. Both mountain belts have eroded greatly over time, “shadows of their former selves,” Nance noted.



When the Atlantic Ocean opened and pushed the pieces of Pangaea apart again, geological evidence of the Rheic Ocean’s line of closure became buried – or was carried half a world away to Europe. That’s why scientists in areas ranging from Texas to Turkey have had to puzzle together remaining scraps of information to reconstruct this sea’s important history.


Nance, for example, has found evidence of the Rheic Ocean in rock formations in Mexico. That also suggests that the range is a bit longer than previously thought, said the scientist, who recently served as an expert on the topic for a National Geographic television program that will air in early 2008.



The creation and break up of supercontinents is one of the hot topics in geological sciences, Nance said, as these major plate movements impact climate change and lead to extinctions. “All hell breaks loose when they get together. When they break up, they are responsible for massive sea level changes,” he said.



The Earth’s land masses have merged into supercontinents at least twice – 300 million years ago to create Pangaea and 1 billion years ago to form Rodinia – and may have done so repeatedly through Earth history. Scientists project that in 250 million years, the closure of the Atlantic Ocean will merge North and South America with Africa and Eurasia, forging what some call “Pangaea Ultima.”



Sound like science fiction? Researchers already see evidence of this future world, Nance said. The Atlantic is about as old and as wide as an ocean can get. As it ages, the floor of an ocean becomes heavier and colder, eventually sinking into the Earth’s interior like a plank of waterlogged wood. Geologists see signs of seabed collapse off Gibraltar and anticipate that the Atlantic floor off the American East Coast and African west coast will be the first to sink.



Learning more about the ancient oceans and continental shifts not only helps scientists predict future geological changes, Nance added, but can suggest where on Earth certain natural resources may lie.



Ancient maps of the world also explain certain synergies in what are now disparate locations – the similar feel of Newfoundland and Scotland, for example, despite their separation by the Atlantic Ocean – and also some surprises. For much of Earth’s history, our Sunshine State was part of Africa. “If it wasn’t for the closure of the Rheic Ocean,” Nance says, “we wouldn’t have Florida. It actually belongs to Mauritania.”

Earth Observation essential for geohazard mitigation





Averaged ground displacements measured on the Etna volcano, using an advanced technique of satellite aperture radar interferometry, using data from ESA's ERS-1 and -2. - Credits: TRE, ESA
Averaged ground displacements measured on the Etna volcano, using an advanced technique of satellite aperture radar interferometry, using data from ESA’s ERS-1 and -2. – Credits: TRE, ESA

Every year geohazards – such as volcanoes, earthquakes, landslides and tsunamis – claim thousands of lives, devastate homes and destroy livelihoods.



In an effort to reduce their impact, more than 250 scientists from around the world gathered for a five-day workshop at ESA’s Earth Observation Centre in Frascati, Italy, to adopt a declaration for an internationally coordinated programme to help save lives and reduce human suffering worldwide.



Because of their unique, panoramic view from space, Earth Observation (EO) satellites can regularly monitor high-risk regions – namely over volcanoes, major landslides and seismic faults. Satellite imagery combined with in-situ measurements make it possible to produce hazard maps, disaster scenarios, forecasts and post-event assessments maps.



“This workshop is very beneficial because it attracts experts from approximately 40 countries in the field of geohazards and allows us to present results of EO applications from our respective countries,” Dr Vernon H. Singhroy, Senior Research Scientist at the Canada Centre for Remote Sensing, said.



“ESA is leading the way in satellite observations and applications for geohazards,” Singhroy continued. “As a community, we learn from the extensive applications of geohazard processes, such as InSAR monitoring, across Europe conducted through ESA programmes.



Data from Synthetic Aperture Radar (SAR) instruments like those flown aboard ESA’s Envisat and ERS-2 satellites are the basis for a technique called SAR interferometry, or InSAR for short. InSAR involves combining two or more radar images of the same ground location in such a way that very precise measurements – down to a scale of a few millimetres – can be made of any ground motion taking place between image acquisitions.



Because very small movements can potentially be detected across tectonic plates grinding past one another or the slow ‘breathing’ of active volcanoes, for example, InSAR has achieved spectacular results in various fields such as the monitoring of volcanoes, earthquakes, landslides and land subsidence.



“The integration of in-situ observations with satellite observations helps us to better understand and forecast specific geological phenomena like volcanoes and seismic sites,” said Jacques Varet, Director of Strategic Planning for Geoscience for a sustainable Earth (BRGM) and Vice President of EuroGeoSurveys. “In-situ observations have a local approach while space-based observations have a global approach. With these communities working together, we integrate our approach and enlarge our horizon.”

Volcanoes



Although there is no way ground-based monitoring can be carried out on all volcanoes across the globe, space-based monitoring helps identify the volcanoes presenting the greatest danger. Satellite radar, such as that aboard ESA’s Envisat and ERS-2 satellites, allows scientists to track small changes in the Earth’s movement and improves their ability to predict volcanic eruptions.



To boost the use of EO data at volcanic observatories, ESA has started to monitor volcanoes worldwide within the framework of the Agency’s Data User Element programme. The Globvolcano project, started in early 2007, will define, implement and validate information services to support volcanological observatories in their daily work by integration of EO data, with emphasis on observation and early warning.


Earthquakes



Shifts in the movement of the Earth’s crust are a hazard in many parts of the world. Using InSAR, scientists are able to detect minute deformations in the Earth’s crust over time, which provides clues as to when an earthquake is imminent.



Interferometry provided a unique insight into the cause of the earthquake in Bam, Iran, in December 2003, which resulted in the deaths of 26 000 people. Studying radar images of the ground around Bam before and after the quake allowed scientists to construct an interferogram and tell geologists in Iran that the fault was actually in a different place than previously thought.


Landslides



Very gradual ground shifts are known to precede major landslides. Often these are on a scale of millimetres – too slight to even be noticed by local observers, but enough to be detected via satellite using radar interferometry.



This technique was the basis of another ESA Data User Element project called Service for Landslide Monitoring (SLAM), which enabled landslide susceptibility mapping across parts of Italy and Switzerland, two of the European countries most under threat.


Declaration adopted



In compliance with GEO (Group on Earth Observations) data policy, scientists have adopted a declaration that, among other requests, calls upon space and in-situ monitoring agencies to release data available over a limited number of high-risk areas. This will allow a better understanding of hazards and allow informed decision making to reduce geological risks.

Measurements link magma melting rate to tectonic plate subduction rate





Craig Lundstrom, a professor of geology, left, and graduate research assistant Fang Huang report new measurements of rock samples from Kick'em Jenny, a submarine volcano in the Caribbean, that link the rate at which magma is produced beneath subduction zone volcanoes to the rate at which tectonic plates converge in this plate tectonic setting. - Photo by L. Brian Stauffer
Craig Lundstrom, a professor of geology, left, and graduate research assistant Fang Huang report new measurements of rock samples from Kick’em Jenny, a submarine volcano in the Caribbean, that link the rate at which magma is produced beneath subduction zone volcanoes to the rate at which tectonic plates converge in this plate tectonic setting. – Photo by L. Brian Stauffer

Determining the origin and rate of magma production in subduction zone volcanoes is essential to understanding the formation of continental crust and the recycling of subducted materials back into Earth’s mantle.



Now, geologists at the University of Illinois report new measurements of rock samples from Kick’em Jenny, a submarine volcano in the Caribbean, that link the rate at which magma is produced beneath subduction zone volcanoes to the rate at which tectonic plates converge in this plate tectonic setting.



“We can use the geochemical measurements to constrain a geophysical parameter, the melt production rate; we then relate the melting rate at an individual subduction zone to its plate convergence rate, which can also be measured,” said Craig Lundstrom, a UI professor of geology. “We can then use this information in similar situations to understand the rate at which magma is produced in other settings.”



Lundstrom and graduate research assistant Fang Huang report their findings in the November issue of the journal Geology, which is published by the Geological Society of America.



The geochemical technique is based on uranium decaying to lead through a long decay chain of short-lived nuclides. For example, U-235 (a “parent” with a half-life of 700 million years) will decay to Pa-231 (protactinium-231: a “daughter” with a half-life of 33,000 years). By measuring the ratio of parent and daughter species in a rock sample (a technique called uranium-series dating), scientists can determine whether the rock is in secular equilibrium (and quite old), or in uranium series-disequilibrium (and very young).


Using multiple-collector inductively coupled plasma-mass spectrometry, Huang and Lundstrom analyzed 12 rock samples from Kick’em Jenny, a submarine volcano located about 8 kilometers north of Grenada in the southern Lesser Antilles arc.



At Kick’em Jenny, the Atlantic oceanic plate is being pushed beneath the Caribbean plate at a rate of 2-4 centimeters per year, one of the lowest convergence rates of any subduction zone.



In Kick’em Jenny lavas, the researchers found there was twice as much protactinium than should be present if the system was in secular equilibrium. This is the largest protactinium-uranium disequilibrium found in any subduction-zone volcano.



The relationship between melting rate and convergence rate centers on the role of water during melting. “An essential part of all volcanoes at subduction zones is the amount of water involved in the mantle melting process,” Huang said. “During subduction, water is released from the subducting slab into the mantle wedge, which lowers the melting point of the rock. When less water is transported to the mantle, less melt is produced.”



At Kick’em Jenny, water is being added very slowly, because the subducting plate is going down very slowly, Lundstrom said. This results in a slower melting rate, which produces a higher ratio of protactinium to uranium 235.



“This is the first study to show that there is a straightforward relationship between this uranium disequilibrium system and the rate of tectonic plate convergence,” Lundstrom said. “No doubt these short-lived nuclides can be used for a variety of other processes in volcanoes, from determining how fast crystals form to how fast magma moves under mid-ocean-ridge volcanoes.”