Month: May 2018

Landslides Can Cause More Landslides

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One might think that if there was already a landslide in a particular location that there’d be nothing left to make another landslide in the future. Regrettably that is not always the case. Indeed, in some geologic settings evidence of a preexisting landslide plays a role in the mapping of future landslide hazards. The deadliest individual landslides in the U.S. recently were in places where there had previously been a landslide. In the small beach community of La Conchita, CA, just south of Santa Barbara along Highway 101, a landslide occurred in 1995 followed by a debris flow in 2005, killing 10 people and damaging 36 homes. In Oso, WA situated next to the North Fork of the Stillaguamish River about 50 miles SW of Seattle, a 2006 landslide was reactivated in 2014 as a debris-avalanche flow that killed 43 people and damaged private property and local highways. A few months later a large rock avalanche near the remote town of Collbran, Colorado occurred from the location of a preexisting rockslide, resulting in the deaths of 3 people. These are just a few examples of many repeat landslides that have been observed.

(Map of Puget Sound Washington, showing the location of the field site in Mukilteo. The gray hillshade inset shows a digital elevation map with the location of the two hillslope monitoring sites, labelled LS and VH.)

USGS landslide scientists Ben Mirus, Joel Smith, and Rex Baum have been studying the coastal bluffs of Puget Sound, WA near Mukilteo where landslides often interrupt railway service. They instrumented two contrasting hillslopes: a steep but stable slope with dense vegetation, and another nearby slope that had experienced a recent landslide. They installed various sensors at 5 locations down the two slopes and waited for rain. They monitored the slopes and collected data for one year and then analyzed what they had. They were curious whether their data might show why landslides were happening in the same place they had before, instead of on nearby slopes that appeared to be just as likely, if not more likely, to slide.

(Topography and aerial imagery of the two slopes LS and VH with locations of the monitoring instrumentation. The top slope, LS, is the one with a previous landslide, and the bottom slope, VH, is the one without a landslide.)

From their measurements, they were able to tell that there were a couple of reasons why the no-landslide location remained stable compared to the preexisting landslide location that remained unstable. Not only did the non-landslide slope have roots from vegetation that stabilized the soil, but also the vegetated slope drained better after rainstorms, shedding the water that would otherwise make the slope more unstable and landslide-prone. The preexisting landslide slope, on the other hand, with less vegetation and roots, had more unstable soil made even more so by the moisture that stayed in the soil after a rainfall, rather than draining away. Repeated rainfalls added more and more moisture to the slope, increasing the instability and potential for a landslide during the wet season.

So despite intuition that a landslide might mitigate further landslides, the disruption by a landslide can actually create a situation that makes the slope even more unstable and prone to further landsliding.

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Modeling Landslide Threats in Near Realtime

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For the first time, scientists can look at landslide threats anywhere around the world in near real-time, thanks to satellite data and a new model developed by NASA. The model (Landslide Hazard Assessment for Situational Awareness (LHASA)), developed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, estimates potential landslide activity triggered by rainfall. Rainfall is the most widespread trigger of landslides around the world. If conditions beneath Earth’s surface are already unstable, heavy rains act as the last straw that causes mud, rocks or debris or all combined – to move rapidly down mountains and hillsides.

(A new model has been developed to look at how potential landslide activity is changing around the world. A global Landslide Hazard Assessment model for Situational Awareness (LHASA) has been developed to provide an indication of where and when landslides may be likely around the world every 30 minutes. Credits: NASA’s Goddard Space Flight Center/ Joy Ng)

The model is designed to increase our understanding of where and when landslide hazards are present and improve estimates of long-term patterns. “Landslides can cause widespread destruction and fatalities, but we really don’t have a complete sense of where and when landslides may be happening to inform disaster response and mitigation,” said Dalia Kirschbaum, a landslide expert at Goddard and co-author of the study. “This model helps pinpoint the time, location and severity of potential landslide hazards in near real-time all over the globe. Nothing has been done like this before.”

The model estimates potential landslide activity by first identifying areas with heavy, persistent and recent precipitation. Rainfall estimates are provided by a multi-satellite product developed by NASA using the NASA and Japan Aerospace Exploration Agency’s Global Precipitation Measurement (GPM) mission, which provides precipitation estimates around the world every 30 minutes. The model considers when GPM data exceeds a critical rainfall threshold looking back at the last seven days.

Landslide changes

(This animation shows the potential landslide activity by month averaged over the last 15 years as evaluated by NASA’s Landslide Hazard Assessment model for Situational Awareness model. Here, you can see landslide trends across the world. Credits: NASA’s Goddard Space Flight Center / Scientific Visualization Studio)

In places where precipitation is unusually high, the model then uses a susceptibility map to determine if the area is prone to landslides. This global susceptibility map is developed using five features that play an important role in landslide activity: if roads have been built nearby if trees have been removed or burned, if a major tectonic fault is nearby, if the local bedrock is weak and if the hillsides are steep. If the susceptibility map shows the area with heavy rainfall is vulnerable, the model produces a “nowcast” identifying the area as having a high or moderate likelihood of landslide activity. The model produces new nowcasts every 30 minutes.

“The model has been able to help us understand immediate potential landslide hazards in a matter of minutes,” said Thomas Stanley, a landslide expert with the Universities Space Research Association at Goddard and co-author of the study. “It also can be used to retroactively look at how potential landslide activity varies on the global scale seasonally, annually or even on decadal scales in a way that hasn’t been possible before.”

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May the Forest Be With You: GEDI Moves Toward Launch to Space Station

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A first-of-its-kind laser instrument designed to map the world’s forests in 3-D is moving toward an earlier launch to the International Space Station than previously expected. The Global Ecosystem Dynamics Investigation – or GEDI, pronounced like “Jedi,” of Star Wars fame – the instrument is undergoing final integration and testing this spring and summer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The instrument is expected to launch aboard SpaceX’s 16th commercial resupply services mission, targeted for late 2018. GEDI is being led by the University of Maryland, College Park; the instrument is being built at NASA Goddard.

“Scientists have been planning for decades to get comprehensive information about the structure of forests from space to deepen our understanding of how this structure impacts carbon resources and biodiversity across large regions and even globally, as well as a host of other science issues,” said Ralph Dubayah, GEDI principal investigator and a professor of geographical sciences at the University of Maryland. “This is why seeing the instrument built and racing toward launch is so exciting.” From its perch on the exterior of the orbiting laboratory, GEDI will be the first space-borne laser instrument to measure the structure of Earth’s tropical and temperate forests in high resolution and three dimensions. These measurements will help fill in critical gaps in scientists’ understanding of how much carbon is stored in the world’s forests, the potential for ecosystems to absorb rising concentrations of carbon dioxide in Earth’s atmosphere, and the impact of forest changes on biodiversity.

GEDI will accomplish its science goals through an ingenious use of light. The instrument is a lidar, which stands for light detection and ranging. It captures information by sending out laser pulses and then precisely measuring the light that is reflected back.

(From its perch on the exterior of the orbiting laboratory, GEDI will be the first space-borne laser instrument to measure the structure of Earth’s tropical and temperate forests in high resolution and three dimensions. Credits: NASA’s Goddard Space Flight Center)

GEDI’s three lasers will produce eight ground tracks – two of the lasers will generate two ground tracks each, and the third will generate four. As the space station and GEDI orbit Earth, laser pulses will reflect off clouds, trees and the planet’s surface. While the instrument will gather height information about everything in its path, it is specifically designed to measure forests. The amount and intensity of the light that bounces back to GEDI’s telescope will reveal details about the height and density of trees and vegetation, and even the structure of leaves and branches within a forest’s canopy.

NASA has flown multiple Earth-observing lidars in space, notably the ICESat (Ice, Cloud and land Elevation Satellite) and CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) missions. But GEDI will be the first to provide high-resolution laser ranging of Earth’s forests.

“GEDI originally was scheduled to launch aboard a resupply mission in mid-2019, but the team at Goddard who is building and testing GEDI was always on track to deliver a finished instrument by the fall of this year,” said Project Manager Jim Pontius, making the move to an earlier resupply mission feasible. The team is now preparing to put GEDI through a battery of pre-launch tests to ensure it is ready to withstand the rigours of launch and operating in space.

NASA selected the proposal for GEDI in 2014 through the Earth Venture Instrument program, which is run by NASA’s Earth System Science Pathfinder (ESSP) office. ESSP oversees a portfolio of projects ranging from satellites, instruments on the space station, and suborbital field campaigns on Earth that are designed to be lower-cost and more focused in scope than larger, free-flying satellite missions.

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