Heat and Rock Stability?

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 Little Rascal 19 Jul 2022

I seem to remember that some of the Welsh slate was badly affected by the heat a summer or two back. Presumably heat expansion/contraction as a form of erosion.

Does this affect any other rock types?

 Offwidth 19 Jul 2022
In reply to Little Rascal:

An absolutely amazing rock factor in heat is how onion skins on granite domes 'breathe'.

https://www.latimes.com/science/sciencenow/la-sci-sn-yosemite-rockfalls-hea...

In reply to Little Rascal:

https://www.bbc.co.uk/news/uk-england-dorset-62160652

Also curious as to the mechanism behind it.

 Ciro 19 Jul 2022
In reply to featuresforfeet:

> Also curious as to the mechanism behind it.

Not a geologist, but I'd imagine prolonged hot dry spells would cause shrinkage in places that usually hold a certain amount of water, creating space for objects that are normally bound in place to start moving.

4
In reply to featuresforfeet:

maybe its a bit like making a sandcastle out of dry sand vs damp sand. dry one will crumble if disturbed. 

OP Little Rascal 19 Jul 2022

Thanks for the links - I had forgotten about granite.

I wondered if the low moisture content of grit would be a factor? Seeing as wet rock is more fragile.  Or exfoliation of flakes in these unprecedented temps?

 Brown 19 Jul 2022
In reply to Little Rascal:

I watched the big wall in the lost world fall down in 2018 and can confirm it was a seriously hot day. It had been making very strange noises for a significant amount of time before it went.

I wasn't quick enough to film it all but got the aftermath on camera from our position on the Dinorwic Unconquerables.

https://www.instagram.com/p/BkviPJzDPBi/?igshid=YmMyMTA2M2Y=

 earlsdonwhu 19 Jul 2022
In reply to Little Rascal:

Form.of weathering rather than erosion.

 balmybaldwin 19 Jul 2022
In reply to Ciro:

Exactly this. Land heave and Subsidence tend to occur around heat cycles (although there can be other causes)

OP Little Rascal 20 Jul 2022
In reply to earlsdonwhu:

Ah yes, thanks for the correction.

 earlsdonwhu 20 Jul 2022
In reply to Little Rascal:

Once a geography teacher.......

 wbo2 20 Jul 2022
In reply to Ciro: I think it more likely that it's heat expansion, including pore water, that is the cause.  But anything happening along a fracture plane, being drying, water going, expansion, tends to weaken it

 Martgib 20 Jul 2022
In reply to Little Rascal:

Squamish's granite experienced a lot of rock fall last summer after extreme heat. Really scary!

https://www.squamishchief.com/local-news/for-the-fourth-time-this-year-a-ma...

 Andy Moles 20 Jul 2022
In reply to Little Rascal:

Cracks in the desert can change width noticeably within the course of a single day - snug locks become tips, gear that was stuck comes out no problem.

I'd have been sceptical of this if I hadn't experienced it first hand!

Extrapolating that kind of change to areas of instability, it's not hard to imagine...

 Trangia 20 Jul 2022
In reply to Little Rascal:

I understand that the granite of the Spitzkoppe in Namibia

https://en.wikipedia.org/wiki/Spitzkoppe

is very brittle and flakey due it's being in one of the driest and hottest places on Earth

 magma 22 Jul 2022
In reply to Trangia:

possibly triggered by heat? youtube.com/watch?v=yAZ1V_DJKV8&

 timparkin 23 Jul 2022
In reply to magma:

> possibly triggered by heat? youtube.com/watch?v=yAZ1V_DJKV8&

I was just about to post that video...  here's a little news article about it

youtube.com/watch?v=wJUHq6nX1iE&

We had a bunch of what we think was this happening at Etive Slabs a couple of years ago 

 timparkin 23 Jul 2022
In reply to Little Rascal:

> I seem to remember that some of the Welsh slate was badly affected by the heat a summer or two back. Presumably heat expansion/contraction as a form of erosion.

> Does this affect any other rock types?

Possible faster erosion of existing rockfall sites could be triggered by rapid temperature rises? Hallett Peak in Rocky Mountain National Park had an epic slide recently 

youtube.com/watch?v=Gu9OTDS3a6g&

 magma 23 Jul 2022
In reply to timparkin:

impressive. looks like a rotational slump possibly triggered by meltwaters?

 Holdtickler 24 Jul 2022
In reply to timparkin:

Wow! puts choss in perspective!

In reply to Andy Moles:

I experienced the opposite at Baggy Point once. We were climbing on Long Rock which, being early in the morning, was out of the sun. Once the sun got on it it took only minutes for the temperature to rise 10 or maybe 15 degrees and then there was an outbreak of swearing seconds trying to remove gear that had become welded in place by expansion - whether of the rock or the gear was unclear. 

 Toerag 25 Jul 2022
In reply to Little Rascal:

All rocks will expand/contract in heat/cold, with the more extreme changes in temperature giving the highest risk of failure.


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