Tag Archives: Planetary science


The Sound of Sliding

December-2013-coverWhen a landslide tore through a remote Alaskan valley in July, no one was there to bear witness. But hours later, geoscientist Colin Stark of the Lamont-Doherty Earth Observatory spotted the event in the pattern of seismic waves passing through the Earth’s crust. Within days, using data from earthquake sensors and satellite images, he and colleague Göran Ekström were able to estimate, from their lab in New York, the landslide’s size, and even determine its path.

The forces generated by landslides aren’t as well understood as those that occur during earthquakes, partly because landslides often strike unpopulated areas with no observers. As a result, landslides leave few clues to how they unfold, making it difficult to predict them or prevent damage the next time.

When humans do live nearby, the consequences can be dire. In 2000, a landslide on the Chinese-Indian border went unnoticed. The rubble created a dam that broke a few months later, killing about 130 people. With better tools for understanding how landslides evolve, where they flow and why some parts of slopes crumble as they do, “these people would not have died,” Stark says.

Ekström and Stark’s collaboration began when Ekström was investigating an apparent series of earthquakes in Taiwan. The seismic data generated by the quakes seemed odd, so he approached Stark, an expert on landslides in the region. To understand the unfolding event better, they created an algorithm combining data from satellite imagery and the international network of seismic stations. The algorithm showed the event was not an earthquake at all, but a series of landslides.

Soon, Ekström and Stark expanded their work to investigate landslides elsewhere. To trace the footsteps of a landslide, they begin by using seismic waves to calculate its force. Then they overlay satellite images to see how far the rubble traveled. Using these parameters, they can calculate a landslide’s mass and acceleration — information otherwise impossible to glean, even for those videotaping the event.

Recently the two used their method to unearth crucial clues about 29 known landslides and discover previously unknown events, including a series of seven landslides in India in 2010. This kind of knowledge, they say, could eventually help researchers — and residents — steer clear of danger in advance of an event.
First published in the December 2013 Discover Magazine [html] [pdf]



Cave detective hunts for clues to past sea level

A yellow splash of light from Bogdan Onac’s headlamp bounces around the dripping orange walls of a cave like a frenetic firefly. At the other end of the beam, the University of South Florida paleoclimatologist explains that the walls of this cave, on the Mediterranean island of Majorca, have collected a bathtub ring of minerals as brackish water washes in and out. “Majorca is like a Gruyère,” Onac says, its underlying limestone filled with holes just like the cheese.

Unlike most coastal cave sites around the world, Majorca sits on a stable tectonic plate and so can serve as a fixed point from which to measure the rise and fall of the sea over time. its caves became encrusted with marine minerals over the course of half a million years. High water marks remain, like graffiti from a changing climate.

A surprise in these cave walls has put Onac at the center of a debate about past sea levels. encrustations dating back 81,000 years at several of his research sites sit about a meter above present-day sea level, suggesting that’s how much higher the seas were then. This contradicts estimates of past sea levels…

See the rest of this profile, these photos, and more in Science News Prime: [html] [pdf]


The Soot Surveyor

In the atmosphere, soot traps heat like carbon dioxide does. But unlike CO2, soot stays near its source and falls to Earth in weeks, so it’s considered low-hanging fruit in the fight against global warming. The first step to reducing atmospheric soot is to find it, which scientists have been doing since the 1980s with a particle-measuring tool called an aethalometer.

A tube catches outside air and sends it to the instrument’s main box, where the air passes through a particle-catching filter. The device shines light of different wavelengths through the filter, and a sensor and processor analyze how the particles block light. This reveals their concentration and their origin: whether they came from fossil fuel burning or wood fires.

Earlier this year, Slovenian pilot Matevž Lenarčič flew around the world with a small aethalometer prototype that Aerosol—a company that makes environmental instruments—might adapt to hitch a ride on commercial flights. Scientists could send such devices on many existing routes, producing the most detailed soot map to date.

To limit emissions while he flew across the globe measuring soot, pilot Matevž Lenarčič tweaked both his flight path and his plane. Flying high reduces drag, but thin air has less oxygen for a combustion engine. So Lenarčič replaced his Pipistrel Virus’s stock engine with a turbo one to get enough power at high altitudes (he hit 29,413 feet next to Everest). For endurance while crossing oceans, he added fuel tanks to the wings. Lenarčič averaged 36.8 miles per gallon, about double the typical efficiency of small planes.

First published by Popular Science in November 2012 [pdf] and published online as “Circumnavigating The World To Map The Polluted Skies” [html]


Carbon Sampling Takes Flight

Last month, aerial photographer and biologist Matevž Lenarčič flew a single-seat airplane across 2000 kilometers of airspace between Easter Island and Totegegie Airport in French Polynesia (right). That lonesome leg was one hop on a 3-month journey around the world, during which Lenarčič and his tiny, lightweight aircraft, a Pipistrel Virus (inset), also touched down on Antarctica, a rare solo feat. Between piloting the plane and collecting photographs for an upcoming book on water, Lenarčič has also collected data on black carbon, or soot, concentrations in the atmosphere. His 290-kilogram plane carries a much-lighter-than-normal Aethalometer, designed by aerosol scientist Griša Močnik of Aerosol in Ljubljana, Slovenia, that measures the optical absorption of the atmosphere and converts it to a rough estimate of soot concentration.

Močnik, whose Aethalometers are already used worldwide at ground stations, hopes to learn enough from Lenarčič’s flight to build instruments capable of riding piggyback on pleasure flights flown by other aviators: “One could build essentially an ad hoc network of instruments … in airplanes [whose operators] would voluntarily participate,” he says.

Aerosol scientists such as Ryan Spackman of the National Oceanic and Atmospheric Administration in Boulder, Colorado, already use much more sensitive instruments mounted on Gulf Stream jets to collect black carbon data—but such flights are expensive for scientists. Small private aircraft could help fill in a lot of data gaps, particularly at low altitudes near urban areas where soot concentrations tend to be high enough for an Aethalometer to provide very good data, Spackman says. “The first few kilometers [above ground level] are the most interesting.”

See this Random Sample in Science Magazine: [html] [pdf]