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Crag & Route Beta

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VIC Arapiles	(General)	(General)	(General)	[ Arapiles Guide \| Arapiles Images ]

Topic Date User

Cracks at Araps 19-May-2010 At 1:10:05 PM gdawg

Message

Thanks Eduardo.

I will begin to form my answer by saying .... WIKIPEDIA.

Plugs, sills, dykes, and even surface lavaflows can all have columnar jointing (as can mud - but if you like climbing mud you are a freak!). Smith Rock in oregon has spectacular columns (with corresponding spectacular cracks - ahh) developed in a basalt lava that flodded an ancient river valley. The river then re-eroded the valley exposing the columns.

Columns at an angle are typically formed in lavas due to uneven cooling or development of an irregular surface of the lava as it flows. Its all related to the temperature profile. If the temperature gradient is simple (i.e cold at the top and hot lower down) then the resulting columns will be relatively straight and vertically oriented. If the temperature field is distorted (as is likley to happen at the margins of a hot tongue of lava) then the cooling pattern will be distorted as well as the resulting joint patterns.

The other way they can occur is if the originally vertical columns are tilted by later tectonic activity. I am not sure which of these two cases is true for Mt Coolum.

Here is an example of radial columnar joints from New Mexico:

(photo source:http://www.appstate.edu/~wilsoncg/triassic07.html )