Gravity's effect on landslides: A strike against Martian water

Dec 22, 2011

A pile of sand, gravel, or other granular material takes on a familiar conical shape, with the slope of the pile's walls coming to rest at the static angle of repose. If the material exceeds this angle, it will trigger an avalanche, tumbling down until it comes to rest at the dynamic angle of repose.

Static angles of repose for coarse, angular materials tend to be around 40° from the horizontal, while smooth grains are stable up to 20°. As largely a matter of geometry, grain properties, and internal friction, scientists have assumed these two angles of repose are fixed for a given substance.

Observations of the angles of gully walls on , found to be too shallow for the materials involved, have been used to argue that surface water must have played a part, either lubricating landslides or depositing the material directly.

But research by Kleinhans et al., using the parabolic flight of an airplane to test the effect of gravity on angles of repose, demonstrates that water need not have been present.

As the plane followed its roller coaster style path, slowly rotating cylinders containing different materials experienced one tenth of Earth's gravity (0.1 g), Martian gravity (0.38 g) and the Earth's normal pull (1 g). The authors find that at 0.1 g, the static angle of repose for all materials increases by 5°, while the dynamic angle of repose decreases by 10°.

They suggest weaker gravity would reduce internal friction for avalanching material and could explain the shallow gully walls on the Martian surface. Further, as angles of repose are commonly used as measures of material properties, this challenge to their presumed independence will require a reassessment of many other surface processes at lower slopes.

Explore further: NASA's space station Robonaut finally getting legs

More information: "Static and dynamic angles of repose in loose granular materials under reduced gravity" Journal of Geophysical Research-Planets, doi: 10.1029/2011JE003865, 2011

add to favorites email to friend print save as pdf

Related Stories

The scars of impacts on Mars

Mar 04, 2011

ESA's Mars Express has returned new images of an elongated impact crater in the southern hemisphere of Mars. Located just south of the Huygens basin, it could have been carved out by a train of projectiles ...

Testing Orion space capsule

Dec 14, 2011

(PhysOrg.com) -- Testing continues at NASA Langley Research Center as the 18,000-pound (8,165 kg) Orion test article took its eight and final splash of the year into the Hydro Impact Basin on Dec. 13. Orion, ...

Recommended for you

NASA's space station Robonaut finally getting legs

7 hours ago

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Sun emits a mid-level solar flare

Apr 18, 2014

The sun emitted a mid-level solar flare, peaking at 9:03 a.m. EDT on April 18, 2014, and NASA's Solar Dynamics Observatory captured images of the event. Solar flares are powerful bursts of radiation. Harmful ...

Impact glass stores biodata for millions of years

Apr 18, 2014

(Phys.org) —Bits of plant life encapsulated in molten glass by asteroid and comet impacts millions of years ago give geologists information about climate and life forms on the ancient Earth. Scientists ...

The importance of plumes

Apr 18, 2014

The Hubble Space Telescope is famous for finding black holes. It can pick out thousands of galaxies in a patch of sky the size of a thumbprint. The most powerful space telescope ever built, the Hubble provided ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

SleepTech
not rated yet Dec 22, 2011
Well that's no fun! Send a probe anyway.
Shootist
1 / 5 (1) Dec 22, 2011
They suggest weaker gravity would reduce internal friction for avalanching material and could explain the shallow gully walls on the Martian surface.


Where are the gullies on the Moon?
nkalanaga
not rated yet Dec 23, 2011
Where are the dunes and other granular deposits for them to form in? Dust and sand on the Moon either forms from impacts or falls from space. It doesn't pile up in unstable heaps from wind deposition, so there's nothing for the gullies to form in.

More news stories

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Cosmologists weigh cosmic filaments and voids

(Phys.org) —Cosmologists have established that much of the stuff of the universe is made of dark matter, a mysterious, invisible substance that can't be directly detected but which exerts a gravitational ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

A homemade solar lamp for developing countries

(Phys.org) —The solar lamp developed by the start-up LEDsafari is a more effective, safer, and less expensive form of illumination than the traditional oil lamp currently used by more than one billion people ...