Volcanos, geology question

[MG1962]

I have a couple of questions about volcanos. I have been hunting around the internet trying to find a forum, but have failed miserably:(

Is it correct that material erupted from a volcano has a unique chemical signature. So if a geologist as handed a sample of this material, they could tell which volcano the sample came from.

Does this signature change over reasonably short periods of time. Example a sample from an eruption in 1000AD and 1000BC be esentially the same?

If they stay the same, could the geologist with two pieces of basalt determine which was older. I have a vague memory that they can test radioactive isotopes, but dont trust myself that I am right

Finally in layman terms, if my assumptions are correct what does a geologist look for when doing these tests

[fishbob]

I have a couple of questions about volcanos. I have been hunting around the internet trying to find a forum, but have failed miserably:(

Is it correct that material erupted from a volcano has a unique chemical signature. So if a geologist as handed a sample of this material, they could tell which volcano the sample came from.

Does this signature change over reasonably short periods of time. Example a sample from an eruption in 1000AD and 1000BC be esentially the same?

If they stay the same, could the geologist with two pieces of basalt determine which was older. I have a vague memory that they can test radioactive isotopes, but dont trust myself that I am right

Finally in layman terms, if my assumptions are correct what does a geologist look for when doing these tests

1 Vulcanologists are kinda strange.

2 A real geologist handed a sample of volcanic material will most likely just toss it.

3 Given 1 and 2 above, I seem to recall that magma chamber chemistry can change quite rapidly, samples from 2000 years apart could be quite different.

4 The relative age of two pieces of basalt can be determined in a variety of ways. Which one was on top? Magnetic anisotropy. Maybe chemistry. Not certain about radioactive isotopes - I seem to recall that the radioactive components of most volcanic minerals have pretty long half-lives, so determination of only a few thousand years might be beyond the resolution of these analyses.

[Aepervius]

Although I am not sure whether the chemical composition change rpidely, there are different type of volcanoe, some giving basaltic lava, etc... It seems that wiki concur, also it does not seem to be specific enough for what you have in mind : wiki volcanoe lava type (http://en.wikipedia.org/wiki/Volcano#Erupted_material)

[Esperdome]

Depends on how many aliens were stuffed down it before the H-bomb went off. ;)

Seriously, good questions. I await answers from more informed posters here.

[Soapy Sam]

I have a couple of questions about volcanos. I have been hunting around the internet trying to find a forum, but have failed miserably:(

Is it correct that material erupted from a volcano has a unique chemical signature. So if a geologist as handed a sample of this material, they could tell which volcano the sample came from.

Does this signature change over reasonably short periods of time. Example a sample from an eruption in 1000AD and 1000BC be esentially the same?

If they stay the same, could the geologist with two pieces of basalt determine which was older. I have a vague memory that they can test radioactive isotopes, but dont trust myself that I am right

Finally in layman terms, if my assumptions are correct what does a geologist look for when doing these tests

Technology changes fast. Kitten is probably the most up to date JREF person on this, but the answer as I recall is that while lavas (and other igneous rocks associated with volcanoes) do fall into types, it's improbable that a sample could be reliably assigned to one particular volcano, except for a few very distinctive types.

But, different geological environments do tend (on average) to yield distinct lava types. For example, submarine lavas are mostly basalts with a fairly distinct chemical range, so if you handed me a lump of syenite, and asked if it came from Krafla or the Azores, I'd say the latter, but if it was basalt I'd go for Krafla. Andesites tend to come from subduction zone volcanoes, so given a sample and asked is this from Glencoe, Nevados de Chillan or Askja, I'd bet one of the first two.
"There's no subduction zone under Glencoe!" I hear you say.
Not now there ain't. Was once though. Or nearby anyway.

But volcanoes (or magma chambers) have a life-cycle and the chemistry of lavas will vary in one place over time.

If you wanted to tell whether a lava came from one of several adjacent volcanoes, simple mapping might give an answer.

So - yes in big, broad environments, and yes in some cases from specific sites, but no , overall, or at least not reliably.

[CapelDodger]

I gather it's possible to identify the detritus from a particular eruption, but that's just something I picked up on Discovery Channel.

[MG1962]

Technology changes fast. Kitten is probably the most up to date JREF person on this, but the answer as I recall is that while lavas (and other igneous rocks associated with volcanoes) do fall into types, it's improbable that a sample could be reliably assigned to one particular volcano, except for a few very distinctive types.

But, different geological environments do tend (on average) to yield distinct lava types. For example, submarine lavas are mostly basalts with a fairly distinct chemical range, so if you handed me a lump of syenite, and asked if it came from Krafla or the Azores, I'd say the latter, but if it was basalt I'd go for Krafla. Andesites tend to come from subduction zone volcanoes, so given a sample and asked is this from Glencoe, Nevados de Chillan or Askja, I'd bet one of the first two.
"There's no subduction zone under Glencoe!" I hear you say.
Not now there ain't. Was once though. Or nearby anyway.

But volcanoes (or magma chambers) have a life-cycle and the chemistry of lavas will vary in one place over time.

If you wanted to tell whether a lava came from one of several adjacent volcanoes, simple mapping might give an answer.

So - yes in big, broad environments, and yes in some cases from specific sites, but no , overall, or at least not reliably.

Thanks for that. I was actually working on a story whereby a strange piece of basalt turns up in a very odd place. The idea being, the basalt was quaried and used in building a temple on Santorini before the big eruption in 1600 BC, and the piece was ejected from the site during the eruption.

So looks like I am going to have to try and find a work around fix

[Soapy Sam]

More likely to be andesite.

[MG1962]

More likely to be andesite.

Thank you - I just looked that up. It might narrow the investigation for my story quiet a bit

[Macoy]

I believe the andesite from the Silver Hills area of Montserrat (millions of years old) is chemically identical to that being churned out by the Soufriere Hills (the other end of the island) eruption, ongoing even as we speak.