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Author Topic: What would be the ash-depth in Dallas if Yellowstone erupted?  (Read 12527 times)

Offline MountainOkie

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hello, I have a coupla questions.....if any of y'all can help, it would be greatly appreciated

1:  what would the ashfall depths be around Dallas in a worst case scenario eruption?

2:  does this map actually reflect real actual evidence that geologists have found; and if so, who came up with the map/did the research?  or is the map just theoretical speculation?

newbielink:http://www.earthmountainview.com/yellowstone/YellowstoneFalloutAshBed.gif [nonactive]

thank you very much for y'alls help!
« Last Edit: 05/02/2012 09:48:47 by chris »


 

Offline JimBob

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Bass, living not all that far from Yellowstone and a noted Yellowstone lecturer, would probably ask for specifics before answering this question. That is: How BIG an eruption are you looking at? There are many eruptions of fumarole and geysers every day, counted in the number of eruptions at extremely low volume and non-productive of ash. Do you want an answer for an eruption of approx. the same size as the map area attached to you post?

BTW How do you like the Broken Bows?
 

Offline CliffordK

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Unfortunately the charts I'm seeing don't show depth of ash deposited with the ash plume.

I'm seeing notes that Yellowstone has erupted with:
2.1 million years ago, ejected 588 cubic miles (2,450 km³) of volcanic material
1.2 million years ago ejected 67 cubic miles (280 km³) of material
640,000 years ago, ejected 240 cubic miles (1,000 km³) of material

The 1980 Mt. St. Helens eruption ejected about 1.2  km³ of material.

Many eruptions are preceded by increased rapidity of bulging of the mountain before an eruption, and there were notes of an acceleration of the bulging in Yellowstone over the last decade, but slowing again recently.

Many mountains seem to go through cycles of mountain building, and cataclysmic explosions, followed by more rebuilding.  However, I see notes that the Yellowstone hotspot may be drifting and thus it may be able to eject new material without the rebuilding phase.

http://en.wikipedia.org/wiki/Yellowstone_Caldera#Volcanic_hazards


As far as determining the extent of the ash flow, the ash should show up as a layer in many sedimentary rock formations. 

It should be able to be attributed back to the primary event by both correlating time associated with the layers, as well as the composition of the ash.

So, I assume that somewhere in Texas there is some sedimentary rock that shows distinctive layers associated with the Yellowstone eruptions. 

I did see notes that the Mt. Mazama/Crater Lake eruption in Southern Oregon sent an ash layer as thick as 6" in parts of Montana, so the ash can travel significant distances.

However, the main destructive forces would be nearer the volcano.  So, even if Texas got a relatively thick blanket of ash, it would likely be more of a hassle than anything else.  You would likely be reasonably protected by putting a T-Shirt over your head, at least in the short-term.

 

Offline MountainOkie

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thank you for your responses!

sorry for not being more specific JimBob...I was wondering about the ash depth for the large super eruptions like the 3 on the map...

CliffordK...I would also think that it would be a simple matter and long ago established historical fact in regards to how deep the ash layers were....that's why I find it so puzzling that I can't find the info anywhere


also, does anyone know if the "Ash Bed" perimeters shown on the map would mean that was the total extent of the ash fall?  or that was just the first wave of ash and that all the rest was negligent dusting that came down over time from higher up in the atmosphere as it circled the globe?

thank y'all again for your time
 

Offline Geezer

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As long as it's heading for Texarse, who cares?
 

Offline Bass

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It depends (standard answer for a rock-pimp)

The two main factors are the size of the eruption and wind directions in the upper and lower atmosphere.  The last three Yellowstone eruptions ranged from humongous, to really big to huge (2500, 680 and 1000 cubic km).  I've heard that over a foot of Lava Creek (the latest eruption) ash has been found in drill holes in parts of the Gulf of Mexico.  How much of that 12"+ is original and how much is reworked material is anybody's guess. 
Obviously, the ash will be thicker as one gets closer to Yellowstone, but the prevailing wind directions will determine how much ashfall will accumulate at any specific location.  The effect of wind direction is well illustrated on your map with the Mount St. Helens eruption.  For example, Missoula Montana got around 4" of ash, while Hamilton MT, only 45 miles south, got less than 1/2".  However, I suspect an eruption the size of Yellowstone will change global weather (and climate) patterns.
As to the map, I've seen something similar from the USGS and other Yellowstone researchers, so it's probably reasonable.  And as you alluded, the perimeter is not the total extent of ash fall, but rather the significant ashfall.  Ashfall would certainly extend across the entire northern hemisphere, and probably worldwide.  There is probably some research looking at ash deposits in artic and antartic ice that could better answer that question.
One of the problems with measuring ash beds is that they are quickly eroded and reworked, making them thinner to missing in some places and thicker in others.
My research suggests that the next caldera eruption, based on potential size of the caldera, will be similar to somewhat smaller than the last eruption (Yellowstone Caldera).  The good news is that the next Yellowstone cataclysm is still probably thousands to tens of thousands of years in the future.
 

Offline Don_1

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I recall a suggestion that CA, NV, AZ & NM along with the south western half of TX would be missed by the  initial plume from an eruption of Yellowstone, but would be effected by the fall out as it completes it's first circumnavigation of the globe. If memory serves me correct and I understood the thinking behind this scenario, under such circumstances, OR, AK, WA and Canada would get off quite light as the cloud drifts south as it encircles the Earth.

But as Bass suggested, an eruption at Yellowstone could have dramatic effects on the weather system and I think the above was based on current weather systems.
« Last Edit: 07/02/2012 09:57:19 by Don_1 »
 

Offline nn55nn

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Info for ash bed depths from Yellowstone volano
newbielink:http://ngmdb.usgs.gov/Prodesc/proddesc_9153.htm [nonactive]

For Dallas area on the biggest Yellowstone eruption:
Best guesstimate is anywhere from .05m to 0.5m  (a few inches to 18 inches worst case);
At the extremities of range, I suspect depth falls off quite quickly. 
A couple hundred miles could be significant.
So probably favoring the low end of the range: a few inches of ash.
Not really a great deal of samples in the link above.
 

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