We need new definitions for Mars. Snow or ice, a state of frozen water, does not appear to be involved with this event at all. Mudslide would involve water and soil, so that word is not right either, since water is not involved and the only “ice” in the equation is frozen carbon dioxide. This is a most akin to a rock slide.

Great picture, all that aside…

I may be wrong but it looks to me like the “up-picture” portion of the cliff (to your right if you were facing it) is ripe for collapse.

Regarding: “In that time I have noticed that you are very loose with numbers” and “I have noticed that Phil is usually less accurate than seems warranted when he provides these types of conversions”

If you go to the first link Phil provided (linked from “Here is another awesome avalanche”), you will find at http://www.uahirise.org/ESP_016423_2640 that it says:

“The cliff, approximately 700 meters (2000 feet) high is made up of layers of water ice with varying dust content, roughly similar to the polar ice caps on Earth.”

Phil’s phrase “700 meters (2000 feet) high” is an _exact quote_ from the HiRISE webpage!

Didn’t you check on that before you implied that Phil was responsible for the inaccuracy?

(As for omitting “approximately”: the single significant digit conveys that sufficiently, I think.)

Does CO2 expand when it freezes?

As far as I know, water (H2O) is the only substance that expands when it freezes; it’s that property of water that makes it unusual.

Here’s some other stuff you might enjoy: http://www.onemoreproduction.com/video/209.html

38. Chris A. Says:
April 8th, 2010 at 11:52 am

@Darrell E. (#17):
“Why not be a little more accurate and say ‘700 meters (about 2300 feet)’? In this context 300 feet is significant.”

Significant figures. I’m guessing (correct me if I’m wrong, Phil) that Phil only felt like he could trust the first digit of the published value (700 m), so he was only safe to state one significant figure. We teach it to our students, so we better walk the talk!

Well, considering the stated resolution I would guess that the error bars are a bit smaller than that but, that is not what I had in mind anyway. I do understand, and utilize daily, the concept of significant figures, but I really don’t see a problem here with equating the 700 meters to “about 2300 feet”, even if the 7 is the only significant digit. But my main point is along a different tack altogether. We are talking about a conversion from one measuring system to another so that readers that are not familiar with conceiving of distances in meters can understand the magnitude of the value, in effect saying that 700 meters equals ___ feet. I have noticed that Phil is usually less accurate than seems warranted when he provides these types of conversions. No big deal.

Also, according to the text, most of the ice cap is water ice with some CO2 on top.

The ice fell to the bottom of the cliff, and made the white patch, and dislodged rock and sand, which slid further down the talus slope, dragging air along. Any ice that rolled down the slope was discolored by sand, or may have sublimated on impact.

Maybe.

With this photo, in addition, I speculated that the fall was of an ice chunk, not rock or debris. The white patch at the base of the cliff may be the impact of that ice, with the dust flow from induced air flow and dislodged rock. I do not see that there is a missing chunk of fresh ice on the cliff top, though.

Significant figures. I’m guessing (correct me if I’m wrong, Phil) that Phil only felt like he could trust the first digit of the published value (700 m), so he was only safe to state one significant figure. We teach it to our students, so we better walk the talk!

I agree, GREAT, GREAT, GREAT!!!

“Chemical weathering.

http://adsabs.harvard.edu/abs/2002AGUFM.P12A0357E”

Okay, I think I get that. I’m not a geologist, and it’s been a very long time since I had to wrap my head around that kind of chemistry (I had to look up ‘fugacity’ to make sure I wasn’t being insulted). So please forgive me if I’m too far off base here.

But, would that kind of weathering cause the splitting and fracturing that we see from water-ice? I can visualize the weathering process, eating away at the surfaces of rocks. But can that also destabilize them? And would it do so over such a long section of the cliff? If the resolution given in #30 is correct, and if my assumption of the area which collapsed is also correct, this was a section of cliff at least 230 meters long, probably much longer! That would seem to be a lot of material for chemical weathering to account for.

@ #28 CafeenMan asked:
“Impact releases less-loose debris?”
I didn’t see anything that mentioned this was related to an impact site. But yes, I would expect impacts to create a lot of debris, which would eventually collapse. But the implication here is that the avalanche was caused by erosion activities and I was simply wondering what kinds of erosion.

@rob #20 I finally got to see the ISS/Shuttle with the new array this morning. It’s always been cloudy when I remembered. Predicted at -3.4 it was incredibly bright, stunningly bright. It was like a fireball in the sky and reached max brightness about 15 deg before reaching max alt. Right as it passed near zenith a 737 passed overhead on approach two fingers breadth from it and it was several times brighter than the landing lights. Put poor Venus to frickin’ shame! I watched it all the way down to the clouds over the hills. From about 20 deg down I had to use averted vision.