Monday, March 13, 2006

Ex-Rolling Stone with Moss

One weekend last May I took a long bike ride with my GPS navigator, geocaching. Having logged a cache on Telegraph Mountain in Tyresö, I climbed down the mountainside and came upon this funny rock at N 59 13.311, E 18 21.373.

Can you see what it is? It's not an artefact. It's half an upside-down giant's kettle. (Anyone know what the real English term used by quaternary geologists is? I'm just translating the Swedish word.)

Giant's kettles are common along escarpments in areas once covered by the inland ice, such as Sweden. When the ice melted away, water would stream with great force across cliff faces for absurdly long periods of time. This would frequently set boulders spinning in depressions in the rock, and with time, they would drill down into the rock provided the boulder was made of a harder mineral than the surface it was sitting on.

Giant's kettles vary greatly in size from baking bowls to swimming pools. If you manage to find one that hasn't been emptied, there's often a stone ball at its bottom, the remains of the spinning boulder. Such a stone is without doubt among the dizziest members of the mineral kingdom.

The rock shown in the photo has been part of a kettle somewhere up the mountainside. Half of it has broken off and tumbled down to the foot of the mountain, landing upside-down. I'm thinking it should be possible to find the other half as well.

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Anonymous Geologist said...

I think the real english word you're looking for is pothole.

13 March, 2006 22:57  
Blogger Martin said...

But a pothole is also a hole in the surface of a bad road!?

13 March, 2006 23:10  
Blogger Space babe said...

Now you've really done it. You're gonna get loads of people coming here in the hope of finding information on Kate Moss with some former Rolling Stone-member.

14 March, 2006 12:59  
Blogger Martin said...

Well, cookie, you know I've always wanted to be a celebrity blogger.

14 March, 2006 21:00  
Blogger ScienceWoman said...

Pothole is indeed the word you are looking for, another term to use might be kolk (with an umlaut over the o).

03 April, 2006 23:07  
Blogger Martin said...

Thank you! You sure about "kölk"? There seems to be a type of geological feature called a kolk (no diaeresis), but it's large enough to form lake basins.

"Rainbow Lake was carved out of black bedrock by an extraordinary current, Alt explains, called a 'kolk.'"

03 April, 2006 23:17  
Anonymous Anonymous said...

Pothole is the english term you are looking for.
I also remember a geologist saying the could be called swallow-holes depending on how they formed.

There are some excellent ones along the Niagara escarpment in Ontario.
One in the Niagara gorge you can walk is about 1-1.5m wide and you can climb through.

12 April, 2006 20:53  

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