Category Archives: Earth sciences

Subduction-zone birth may be happening off Portuguese coast

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New Scientist: Subduction zones occur where one tectonic plate is forced under its neighbor until it melts into the mantle. If an ocean lies between the plates, subduction can cause it to be squeezed out of existence within a gigayear. How the zones form is uncertain because the rock involved appears to be too strong to break or be subducted. Now João Duarte at Monash University in Melbourne, Australia, and his colleagues believe they have found an area off the southwestern coast of Portugal that is in the process of becoming a subduction zone. Portugal experienced major quakes in 1755 and 1969, despite the lack of major fault lines in the area. Duarte’s team mapped geological activity off the coast for eight years. They found that the known thrust faults were linked by previously unknown transform faults, resulting in a system of faults hundreds of kilometers long. The reason they think that this is a protosubduction zone is that it is just 400 km away from the Gibraltar Arc, a subduction zone in the western Mediterranean responsible for the shrinking of that sea as Europe and Africa collide. They believe that as the two continental masses approach each other, the subduction zone spreads into nearby areas of tectonic weakness. If they are correct, it could be that the Atlantic Ocean, which is a relatively young ocean, could begin shrinking in the geologically near future.

Melting, not calving, may be driving Antarctica’s ice loss

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Nature: Nearly half of Antarctica’s ice shelves—the portions of the ice sheet that extend over the ocean—are thinning due to warming ocean currents, according to new monitoring data and computer modeling. In fact, some ice sheets are losing more ice from such basal melting than from the calving—or breaking off—of icebergs, once thought to be the primary factor in ice-shelf dynamics. Eric Rignot of the University of California, Irvine, and colleagues, whose paper has been published in Science, also found that about half of the total meltwater comes from just 10 small ice shelves along the southeast Pacific coastline. Despite those losses, other ice shelves are thickening or maintaining equilibrium. Rignot and coworkers’ findings point up the difficulty of projecting long-term ice-sheet evolution because of the many factors involved, including sea-floor topography and ocean circulation, which change over time.

Challenge raised to role of water in behavior of Earth’s mantle

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Nature: The ability of rocks to flow is behind a range of phenomena, including plate tectonics and the convection of the mantle. To better understand rock flow, Hongzhan Fei of the University of Bayreuth in Germany and his colleagues examined individual crystals of olivine, one of the common minerals in Earth’s mantle, under pressures and temperatures similar to those at depths of 100 km to 200 km. They found that silicon was the mineral’s slowest moving atom, which the team believes is the limiting factor in the rocks’ ability to flow. The researchers found that increasing the water content did not significantly increase the silicon atoms’ movement rate, contrary to some previous studies. And it still is not clear whether silicon is actually the determining factor in rock viscosity.

Fight over fracking comes to fore in California

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New Scientist: Hydraulic fracturing—commonly called fracking—is a technique for extracting oil and natural gas from underground rock layers by pumping in water mixed with sand and chemicals. Use of the technique has become more common, but has been criticized for increasing groundwater pollution and causing geologic instability. And in California, which is home to the Monterey Shale Formation, concerns have arisen over potential air pollution. The formation is estimated to hold 1900 million tons of recoverable oil—more than 2.5 times as much oil as in the fields of North Dakota that sparked a boom economy there. However, much of the field is located in densely populated Los Angeles County, which already has high levels of air pollution. A petition was presented to Governor Jerry Brown asking for a statewide ban on fracking, but a bill proposing a moratorium on fracking was recently defeated in the legislature.

Water from rocks in a mine is at least 1 billion years old

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Ars Technica: Deep below Earth’s surface, sediment is compacted and metamorphosed into hard rock. Hydrothermal fluids that bathe the rocks while they are forming can get trapped in fissures. When those rocks are later uncovered by human mining, the water’s age can be determined by examining the ratios of isotopes of noble gases dissolved in the water. With that method, water from a mine near Timmins, Canada, has been determined to have been trapped between 1 billion and 2.6 billion years ago, making it the oldest known water. The key element in the determination was xenon, of which 9 different isotopes were present. Some of those isotopes point to the water’s hydrothermal origin. Others reflect the atmospheric composition of Earth about 1.5–2.6 billion years ago. And the levels of other noble isotopes, which are the products of the decay of radioactive elements, put the date of entrapment anywhere between 1.1 billion and 1.7 billion years ago. Also present in the water were H2 and methane, two compounds necessary for microbial life. That discovery suggests that similar fluids could be preserved on other worlds, such as Mars, and could contain signs of ancient, extraterrestrial life.

Global warming may exacerbate US Southwest’s rainy season

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Science News: As the climate warms, monsoons could become more severe, bringing fewer but heavier rainfalls. In a study published this week in the Proceedings of the National Academy of Sciences, Yemane Asmerom of the University of New Mexico and colleagues analyzed cave formations in the state’s Carlsbad Caverns and compared the data with that from other caves across the Northern Hemisphere. Caves contain clues to past precipitation because features such as stalagmites grow as water seeps into the cave, evaporates, and leaves behind dissolved minerals. What the researchers found was that over long time periods of decades and even centuries, warm weather makes monsoons wetter and cold weather makes them drier. However, because of regional differences such as the concentration of aerosols or types of land surface features, monsoon activity is much less predictable on shorter time scales.

Earthquake hits eastern Russia

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Nature: Perhaps the biggest earthquake ever recorded struck off the coast of Russia on Friday. Although its magnitude was calculated to be 8.3, it caused minimal damage because of its great depth—some 610 km beneath Earth’s surface. The quake originated at the junction of the Pacific and Eurasian lithospheric plates, beneath the floor of the Sea of Okhotsk. Minor tremors were felt as far away as Moscow and northern Japan. Several smaller quakes struck before the large one, but whether they are related has yet to be determined. Geologists began to rethink their theory of deep earthquakes in 1994 when a 636-km-deep quake struck Bolivia; until then, geologists thought earthquakes could not occur so far down because the rock was too hot to rupture quickly.

Navy research submersible finishes $41 million retrofit

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Nature: In 1964 the US Navy commissioned the DSV Alvin, a small, manned research submarine. Since its launch, Alvin has been responsible for several major discoveries such as ecosystems powered by hydrothermal vents instead of sunlight. In 2011, after making observations of the Deepwater Horizon oil spill, the vessel began a $41 million retrofit that has just been completed. On 25 May, Alvin will leave Woods Hole Oceanographic Institution in Massachusetts for a series of certification cruises off the coast of Oregon. Its upgrades include a larger sphere with extra windows and cameras for human occupants, longer manipulator arms, and a larger sample collection container. The new titanium sphere is capable of reaching depths of 6500 m, but the craft will still be limited to its previous maximum depth of 4500 m because its lead-acid batteries are not suitable for the lower mark. Susan Humphries, who was in charge of the retrofit, hopes that lithium-ion batteries will soon be safe enough to be added during regular maintenance in the next 5 years.

Oklahoma tornado surprisingly quick forming and long lasting

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Los Angeles Times: The Oklahoma City suburb of Moore has been hit by major tornadoes in 1999, 2003, and now 2013. Weather experts believe that the tornado strikes are just a case of statistical bad luck and that the town’s specific location does not make it especially prone to storm formation. However, the middle part of the US is called Tornado Alley because it is the meeting area of warm, humid air from the Gulf of Mexico to the south and cool, dry air from the Rocky Mountains to the west. The two masses of air create swirling winds that spawn massive supercell thunderstorms. On the day of the most recent tornado, a lot of warm, moist air lay near the ground, with a quick drop in temperature as altitude increased. And a nearby dissipating storm may have caused a surge of low-level air that fed the circulation driving the storm. The resulting storm developed incredibly quickly, with the supercell forming in 10 to 15 minutes. The tornado itself lasted for 50 minutes and traveled for 20 miles, whereas most tornadoes last less than 10 minutes. Weather scientists hope to use extensive radar measurements and other observational data to try to determine why the tornado formed so quickly.

Iceland expands volcano monitoring capabilities

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BBC: The Icelandic Meteorological Office (IMO) is beginning the installation of an expanded network of monitors and sensors as part of the FutureVolc project. Funded in part by the European Union, the project is a response to the 2010 eruptions of Eyjafjallajökull, which shut down air traffic across Europe. The IMO is adding a range of monitors that will be looking for small movements or tremors in the ground or the curving of Earth’s surface that could indicate a magma buildup. Other sensors will detect changes in gas emissions. All of the installations will provide real-time data to the IMO’s offices in Reykjavik. The IMO hopes to increase its ability to detect imminent eruptions several hours to days early. At many sites, residents are currently lucky to have 1 to 2 hours’ warning. The scientists will also be studying ash types and dispersal patterns to better plan for future air traffic disruptions. An Airbus report says the 2010 eruptions resulted in $5 billion in lost business revenue worldwide.