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Hey, I'm more curious about this than anything. I'm debating a young earth creationist and he's saying that rocks from the Mount Saint Helens eruption - I have to assume newly formed igneous rock - have been dated as being several thousand years old only a mere 30 years after the initial eruption. My common sense is telling me that this is because the Mt. St. Helens eruption was primarily an ash and landslide one, and the rocks spewed up would be fairly recent, even several thousand years old, but I'm curious if anyone could shed a little more light on this situation for me.

Thanks a bunch!

Also, he's providing this article as evidence for his statement. I don't know a whole lot about radiometric dating or its flaws, nor about the scientific communities regarding the rapid recovery of Mt. St. Helens' ecosystem, nor even about how sedimentary rocks form. The article postulates that they can form in hours, although I find this highly unlikely.

Anywho, here's the article.

The article appears to be advocating catastrophism.

To this day, the resulting steep-sided canyon walls can be seen,2 showing that horizontal sediment layers hundreds of feet thick were formed within hours during the eruption. This sparks the question: what other layered sedimentary rocks in earth's crust were formed rapidly?

Not so many. There are signs that tell if sediment was deposited quickly versus slowly. For example, rounded river rocks require erosion to smooth them out which implies deposition over time.

A new rock cap atop the mountain that formed after the 1980 eruption should have shown it to be on the order of tens of years. But standard analysis gave the totally incorrect date of 350,000 years.3 What other rocks have been dated incorrectly by following those standard dating protocols?

This?
http://www.icr.org/article/argon-mount-st-helens/

I am... weary of anything published by their own internal department. Especially since it is claiming that two basic physical principles (radioactive decay/diffusion of gases) are false.

Could the tree bark-rich coal beds have been formed by a catastrophe even more massively destructive than Mount St. Helens?

No. If the situation is destructive enough they will just burn.

Experts at the time of the 1980 eruption predicted that the area would take perhaps hundreds of years to rebound. Yet after only 20 years, biologists noted the speedy recovery of plants and animals on what had been a vast moonscape.6 Today, the 30-year-old blast zone is a lushly treed forest. Creation science models based on the records of Genesis expected to see this happen, since Genesis discloses that God created creatures for the very purpose of “filling” the earth,7 and since after the Flood the creatures aboard the Ark were able to quickly adapt to the new environments produced by the cataclysm.

I should note those "experts" were idiots. For starters, volcanic ash makes a good fertilizer so plant life would regrow quickly. And once you have plants, animals return to eat them. It doesn't prove genesis as God, having alot of time, presumably wouldn't care about how long it took to fill the earth. By contrast if you work of the idea that animals are rational consumers than they will automatically go to new areas in order to maximize their utility- the area would lack competitors and at a certain point the plant growth would be thick enough that derived utility would exceed that from their current area.

Plants, of course, not being concious would simply go were their seeds are deposited. I think the surprise was that seeds can be deposited so far, but part of the reason was that some life survived being buried under the ash.

Because of the Mount St. Helens eruption, scientists know that sedimentary rock layers can form in only hours, rather than requiring millions of years.

They are being dishonest. The sediments already existed- they were just moved around. The layering is new, but if the earth was young it wouldn't have any sedimentary rock to form said layers!

OF COURSE some sediments are deposited very quickly.
What, he actually thinks geologists don't know that? That they just look at any layer of rock and conclude "oh, it must be very old"?

Flood deposits (you know, from local floods?), volcanic ash and some other layers are deposited relatively rapdidly.
Most forms of rock are NOT. Point out chalk cliffs - if they were formed within a year (during the "Great Flood"), then the amount of certain microorganisms would have to be billions of times larger during that time - totally violating thermodynamics and boiling the oceans.

I would look into the potholer54debunks channel, specifically Noahs flood debunked for an elaborated version of what i just said.

That certain volcanic rocks are dated as old after an eruption is no mystery either. These rocks simply form inside the volcano long before the eruption and are ejected without being melted again.
Knowing their age is important, since it allows for better modelling of volcanic lifecycles (you can determine how long the magma was in there, what it's composition was and more).

All radiometric dating has a useful range of dates. You are, after all, counting atoms in fancy ways. This is difficult to do, especially when you are counting atoms at the very edge of the sensitivity of your instruments. Getting a date of a few thousand years, for K-Ar dating, actually indicates that the timescale is too short for the dating method to measure accurately. It's kind of like using a calendar to time a horserace.

Another point to consider is that the 1980 Mt. St. Hellen explosion was a pyroclastic flow, not a lava flow eruption. K-Ar dating measures from the last time the material was in the liquid phase. But in pyroclastic flows, the rock material doesn't get much hotter than 1000 °C, nowhere near hot enough to melt it and reset the K-Ar clock. Thus, that the rocky material dates to several thousand years should be not at all surprising — the dating method has measured something other than the time to the last eruption. You can't just throw a dating method willy nilly at a subject and expect it to work; you have to investigate carefully whether or not the method matches the scenario.

In order for your friend's argument to stick, he has to prove that the dated material was in fact melted during the eruption.