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→You Just Gotta Be Kidding Me
:"''...that my friend is the difference...''": But there is no difference!
:"''...that my friend is the difference...''": But there is no difference!
:[[User:Philip J. Rayment|Philip J. Rayment]] 09:16, 6 February 2008 (EST)
:[[User:Philip J. Rayment|Philip J. Rayment]] 09:16, 6 February 2008 (EST)
::I finally succumbed to one of the bugs that has been going around my wife's school a week ago, so I have been unable to respond to this until now. Apologies. I would like to suggest that schools install sheepdips by the main entrance to make the little buggers more hygenic.
:: Anyway - TerryH, your comments made me groan a great deal. The supposed problems with the age of the old lava dome at Mt St Helens is a very old chestnut that was exploded years ago. Let's start off with basic vulcanology - it is a massive mistake to think that dating a volcanic eruption depends on analysing the lava, as there are some problems with that. For one thing - what on earth makes you think that the lava that is erupting is formed then and there? Mt St Helens is erupting right now, it has been for the past 4 years. So far all its doing is pushing up lava that is identical to the lava of the 1980-1986 eruption. It's basically clearing its throat, before fresher lava comes up (sorry for the metaphor, but it works). That lava was not formed in 1980. It's been down there for a while. That's the way that it works - magma collects in the main magma chamber as it seeps up from far below. Mt St Helens is a part of the Cascades subduction zone - the magma there is the light, relatively frothy rock that was scraped off the ocean crust as it descended below the North American Plate a very long time ago - as much as 500,000 to 1 million years ago. It rose into the magma chamber, pooled there, and was finally erupted. Saying that lava seems to be old for an eruption that happened 20 years ago is merely pointing out the way that vulcanology works - you're actually underlining the fact that this is an old world and that volcanic eruptions are, chemically speaking, not instant events! So thanks, TerryH, you just proved my point!
::As for the so-called problems with the K-AR method, there aren't any. Asking anyone to use the K-AR method to get the age of the 1980-86 eruption is like using Big Ben to measure how tall an ant is. The half-life of potassium-40 is rather long - 1,250 million years. Plus a few thousand years are not enough time for 40Ar to accumulate in a sample at high enough concentrations to be detected and assessed. As a result, the K-Ar method cannot be used to date samples that are much younger than 6,000 years old.
::As I said, this old chestnut has long been exploded. [[User:Darkmind1970|Darkmind1970]] 18:10, 6 February 2008 (EST)