Snapping a Martian Avalanche (APOD 11 Mar 2008)

neufer · Post by **neufer** » Tue Mar 11, 2008 12:59 pm

----------------------------------------
Victor Appleton - _Tom Swift And His Wizard Camera_
Chapter XV. Snapping an Avalanche

<<The sky was covered with lowering clouds, and there were occasionally flurries of snow. Tom's airship was well above the snow line on the mountains. The young inventor and Ned sat in the pilot house, taking observations through a spyglass of the mountain chain below them.

Suddenly Ned, who had the glass focused on a mighty peak, cried out:

"There she is, Tom!"

"What?"

"The avalanche! The snow is beginning to slide down the mountain! Say, it's going to be a big one, too. Got your camera ready?"

"Sure! I've had it ready for the last three days. Put me over there, Ned. You look after the airship, and I'll take the pictures!"

Tom sprang to get his apparatus, while his chum hurried to the levers, wheels and handles that controlled the Flyer. As they approached the avalanche they could see the great mass of ice, snow, big stones, and earth sliding down the mountain side, carrying tall trees with it.

"This is just what I wanted!" cried Tom, as he set his camera working. "Put me closer, Ned."

http://apod.nasa.gov/apod/ap080311.html

Ned obeyed, and the airship was now hovering directly over the avalanche, and right in its path. The big landslide, as it would have been called in this country, met no village in its path, fortunately, or it would have wiped it out completely. It was in a wild and desolate region that it occurred.

"I want to get a real close view!" cried Tom, as he got some pictures showing a whole grove of giant trees uprooted and carried off. "Get closer Ned, and--"

Tom was interrupted by a cry of alarm from his chum.

"We're falling!" yelled Ned. "Something has gone wrong. We're going down into the avalanche!".>>
----------------------------------------

JohnD · Post by **JohnD** » Tue Mar 11, 2008 8:01 pm

Today's APOD text (11/3/8) refers to a HiRise page, where it is claimed that not one, but FOUR avalanches were caught by the Mars Reconnaissance Orbiter http://mars.jpl.nasa.gov/mro/overview/. Go to the HiRise site http://hirise.lpl.arizona.edu/PSP_007338_2640 and click on the underlined phrase that makes this claim, or the subimage hotlink on the right.

That so many occured at the same time makes me ask if there was a small marsquake to trigger the falls. Is there a seismic probe on the planet?

John

JohnD · Post by **JohnD** » Tue Mar 11, 2008 8:07 pm

Moderators,
Er, I think this post could be merged with mine on 'Martian Avalanche'.
I think.
As this has precedence, perhaps mine should be merged with this.
At least I think it's about a Martian avalanche.

Or is it?

John

ta152h0 · Post by **ta152h0** » Tue Mar 11, 2008 8:31 pm

Catching an avalanche on Mar,s as it happens, makes MRO the top celestial papparrazi. that is soo cool. I would submit the glue ( CO2 ice ) turned to WD40 ( CO2 vapour ) and the slab just slid down the hill as it warmed up. Pass the beer

apodman · Post by **apodman** » Tue Mar 11, 2008 9:50 pm

I really don't know which way is up in this image. I can't reconcile the picture with the description of the sun coming from the upper right. I don't know whether I'm supposed to look at the bright cloudy area on the left or the larger darker cloudy area on the right. I'm all mixed up. Please somebody give me a hint.

neufer · Post by **neufer** » Wed Mar 12, 2008 2:01 am

apodman wrote:I really don't know which way is up in this image. I can't reconcile the picture with the description of the sun coming from the upper right. I don't know whether I'm supposed to look at the bright cloudy area on the left or the larger darker cloudy area on the right. I'm all mixed up. Please somebody give me a hint.

Up is 1) where the satellite is and
2) where the high icy (not cloudy) plateau is on the left

Down is where the dust storm (i.e., the larger darker cloudy area on the right) is.

Presumably, the North Polar plateau has rotated clockwise like the earth
and the melting is due to the warm afternoon sun coming from the upper right.

apodman · Post by **apodman** » Wed Mar 12, 2008 3:59 am

Thanks, I'm all aligned now. When I looked at the photo earlier, it just looked flat to me (so real was the 2D rendering). When I look now, I see the great height of the cliff and correspondingly the great depth of the photo. I'd like to see a 3D of this one through one of those old stereo viewers. And I'm sorry I forgot that "up" is on your list of trigger words.

My aging eyes apparently come and go. Usually I see no motion in images like the following one ...

http://www.richrock.com/gifs/optical-il ... tating.png

... but now it's working.

neufer · Post by **neufer** » Wed Mar 12, 2008 2:42 pm

apodman wrote: I'd like to see a 3D of this one through one of those old stereo viewers.

The satellite is programmed to view as much territory as possible and would have to be reprogrammed to view the same area twice. Even if they had accidentally done so for this particular case the avalanche would probably have moved too much between the two photograph to have made for good 3D. OTOH, Martian sand dunes apparently move so slowly (at least between major dust storms) that this March 1999 to April 2001 3D picture was possible:

http://antwrp.gsfc.nasa.gov/apod/ap010815.html

apodman · Post by **apodman** » Wed Mar 12, 2008 11:09 pm

Understanding the impracticality of obtaining the two views necessary for stereo viewing, I still wanted to express my idle wish.

I don't look good in red-and-blues (cardboard retro frames, etc.) so I was thinking more of one of those binocular widgets you place over two side-by-side photographs (not colored nor superimposed) for a kind of ViewMaster effect. They handed them out in Geology class along with books of aerial photos snapped in pairs short distances apart. Cliffs and waterfalls just leaped out of the page at you. (I'm fallllling ...)

shawakanda · Post by **shawakanda** » Thu Mar 13, 2008 5:30 pm

Just to clarify...

HiRISE, which is the instrument that acquired the image containing the avalanche, is commanded by people. Each observation is painstakingly planned by a person at the University of Arizona. Sometimes something surprising is seen in the image, but an image is never acquired without a human deciding to acquire the image. So, humans can react to scientifically valuable observations. The instrument is "dumb" in that it just does what it's told, but its commands are uplinked every couple of days.

The nominal plan for HiRISE is to acquire a few hundred to a few thousand stereo pairs. For example, any future landing site must be observed by HiRISE before it can be certified as safe. Part of that certification often includes stereo observations to get topographic information.

With respect to this particular location on Mars... I expect HiRISE will acquire stereo images. However, more likely is that right now, they will acquire monitoring images to study how the cliff face changes over time. Since it is late northern spring/early northern summer, the frost patterns are changing quickly, so I wouldn't expect a good stereo pair would be acquired until late into summer so a stable stereo pair can be acquired.

--Your friendly martian scientist.

auroradude · Post by **auroradude** » Sat Mar 15, 2008 7:36 pm

That so many occured at the same time makes me ask if there was a small marsquake to trigger the falls. Is there a seismic probe on the planet?

Actually I have observed a similar phenomenon from my home, located out of Homer, Alaska. We live on a ridge and overlook Cook Inlet. The shore has cliffs above that run for several miles. There are layers of coal, sandstone and clay (actually compressed vocanic ash). These layers tend to be topped with layers of sand, gravel, cobbles and boulders from subsiquent periods of glaciation. The water table can be seen to seep out of some of the permiable layers over the impevious all along the cliffs.
During cold spells, well below freezing, I have seen plumes of dust rising from many places all at once. This occurs most in the afternoon sun around 2:00 local time when the sun is most effective. Sunlight is also reflected off the water adding to its effect.
I think it might be caused by the seeping water being frozen and then thawing in the afternoon. It then releases chunks of ice mixed with sand gravel, rocks and boulders. These kick up the dust on the way down the slope.
I know the conditions are not quite the same for Mars as they are here but a similar phenomenon might be at work there too. It could be that the afternoon sun on Mars that is creating the instability - perhaps from sublimating layers of frozen carbon dioxide.
Thus the whole sun-facing slope comes at risk of failure at nearly the same time and it wouldn't require seismic activity of any kind to have multiple avalanches.

neufer · Post by **neufer** » Sat Mar 15, 2008 8:39 pm

auroradude wrote:
That so many occured at the same time makes me ask if there was a small marsquake to trigger the falls. Is there a seismic probe on the planet?
Thus the whole sun-facing slope comes at risk of failure at nearly the same time and it wouldn't require seismic activity of any kind to have multiple avalanches.

[Bart claps]

Lisa Simpson: What are you doing, Bart?

Bart Simpson: Eh, just passing the time.

[Bart claps, snow repeatedly falls on Homer]

Homer Simpson: Aw, my boy loves Alaska so much, he's applauding it. Lisa, why aren't you clapping?

Lisa Simpson: But Dad!

Homer Simpson: Clap for Alaska!
[Lisa claps along with Bart]

Homer Simpson: [Homer is buried under an avalanche]

auroradude · Post by **auroradude** » Sun Mar 16, 2008 2:20 am

DOH!

NoelC · Post by **NoelC** » Sun Mar 16, 2008 6:07 pm

LOL, neufer you are ALL over the (cosmic) map!

-Noel