Just when you were worried about bridge collapse.
October 5, 2015 4:17 AM Subscribe
Geologists use a novel dating technique to find the cause of a tsunami. Single link New Yorker.
Isn't there a similar precarious rock formation under the Atlantic, off the coast of Africa, which, at some point, will fall and produce a tsunami that will wipe out the eastern seaboard of North America?
posted by acb at 5:36 AM on October 5, 2015
posted by acb at 5:36 AM on October 5, 2015
acb: The Canary Islands, yes. Though it sounds like the threat is probably overstated as it's unlikely that a landslide on that scale would be fast and coherent.
posted by irrelephant at 6:05 AM on October 5, 2015 [1 favorite]
posted by irrelephant at 6:05 AM on October 5, 2015 [1 favorite]
but worth noting it is highly speculative.
It could have gripped it by the husk.
posted by three blind mice at 6:08 AM on October 5, 2015 [5 favorites]
It could have gripped it by the husk.
posted by three blind mice at 6:08 AM on October 5, 2015 [5 favorites]
It'd be nice if the article itself weren't behind a paywall. :/
The thing with cosmogenic dating of any stripe is that there are a lot of factors involved in just how much bombardment of cosmic rays a given surface receives, and this can be sensitive to (and require corrections for) things as significant as boulder toppling and erosion or the boulder surface (seems like a decent concern for basalt/limestone--that boulder is awful pretty but is also kind of falling apart) to seemingly-insignificant things like angle of the boulder surface. And I'm sure they brought all of that kind of thing into consideration, but those sorts of things in conjunction with sample size/data set results is, in my opinion, really important in weighing just how solid their conclusion is.
Anyway "conclusively identified" is a pretty strong way to end an article and I'm hoping maybe after work I can get my hands on the actual data. Still cool though. I tend to associate landforms/boulders created/deposited by catastrophy-type events mostly in the context of big mountains, but then again that's mostly what I've worked with. Anytime you get tectonic plates involved it's not an unreasonable culprit to think about.
posted by nogoodverybad at 6:16 AM on October 5, 2015 [1 favorite]
The thing with cosmogenic dating of any stripe is that there are a lot of factors involved in just how much bombardment of cosmic rays a given surface receives, and this can be sensitive to (and require corrections for) things as significant as boulder toppling and erosion or the boulder surface (seems like a decent concern for basalt/limestone--that boulder is awful pretty but is also kind of falling apart) to seemingly-insignificant things like angle of the boulder surface. And I'm sure they brought all of that kind of thing into consideration, but those sorts of things in conjunction with sample size/data set results is, in my opinion, really important in weighing just how solid their conclusion is.
Anyway "conclusively identified" is a pretty strong way to end an article and I'm hoping maybe after work I can get my hands on the actual data. Still cool though. I tend to associate landforms/boulders created/deposited by catastrophy-type events mostly in the context of big mountains, but then again that's mostly what I've worked with. Anytime you get tectonic plates involved it's not an unreasonable culprit to think about.
posted by nogoodverybad at 6:16 AM on October 5, 2015 [1 favorite]
Paywall? I can access it directly with no sign-in. Ah, here it is: six freebies a month. Maybe try a different web browser or new IP address or some combo thereof?
posted by mwhybark at 6:32 AM on October 5, 2015
posted by mwhybark at 6:32 AM on October 5, 2015
Paywall? I can access it directly with no sign-in.
Sorry, I meant the actual study itself.
posted by nogoodverybad at 6:38 AM on October 5, 2015 [2 favorites]
Sorry, I meant the actual study itself.
posted by nogoodverybad at 6:38 AM on October 5, 2015 [2 favorites]
Geologists use a novel dating technique to find the cause of a tsunami
Tinder? Grindr? Ashley Madison?
posted by chavenet at 6:45 AM on October 5, 2015 [7 favorites]
Tinder? Grindr? Ashley Madison?
posted by chavenet at 6:45 AM on October 5, 2015 [7 favorites]
Just when you were worried about bridge collapse.
posted by PeterMcDermott at 7:42 AM on October 5, 2015
posted by PeterMcDermott at 7:42 AM on October 5, 2015
Geologists use a novel dating technique to find the cause of a tsunami
Tinder? Grindr? Ashley Madison?
The dating app for earthquakes ought to be called Temblr.
posted by Strange Interlude at 7:54 AM on October 5, 2015 [8 favorites]
Tinder? Grindr? Ashley Madison?
The dating app for earthquakes ought to be called Temblr.
posted by Strange Interlude at 7:54 AM on October 5, 2015 [8 favorites]
Geologists use a novel dating technique to find the cause of a tsunami
"Inundatr", surely?
posted by Greg_Ace at 8:20 AM on October 5, 2015 [3 favorites]
"Inundatr", surely?
posted by Greg_Ace at 8:20 AM on October 5, 2015 [3 favorites]
irrelephant: This article is arguing that the landslide in question did trigger a “mega-tsunami”, so the comforting arguments made by that geologist may not be all that convincing if we actually have evidence of such an event with-in the last 100k years.
posted by pharm at 8:27 AM on October 5, 2015
posted by pharm at 8:27 AM on October 5, 2015
Although the cosmogenic dating is the point of the New Yorker article is pretty cool, it's becoming "old hat" (in a decade old sense, haha!) enough that there are look-up tables being published in journals like Quaternary Geochronology or Journal of Geophysics frequently for different kinds of exposure surfaces and rock types. (My favorite application I've seen is to use sunlight exposure for dating sand dunes.) The neat thing about a lot of this dating is it can be backed up by dating using paleontological methods and vice versa.
The point of the actual study (to which I have access) was to prove that the boulders are indeed tsunamigenic, or deposited from a tsunami; that dating of the deposits would fit the dating of the collapsed flank of the volcano; and then to calculate wave height and energy to to show that giant, collapse generated tsunamis do exist in the geologic record. Below the boulders in the valleys and slopes are run-up sheets of sand which thin up-slope; chaotic conglomerates and other boulder deposits, and rip-up clasts of various types. Additionally there is the cliff band of basalt, which was a submarine (under sea) lava flow which produces a basalt with a very distinctive joint pattern; dating of the basalt itself showed an origin of ~2.5-2.3 m.y.a., and it was then uplifted. (Part of the study has to deal with how much of the island has been uplifted and when to properly calculate wave height.) Essentially the boulders on top of the plateau are giant rip up clasts where the wave tore rocks from that cliff band of lava. And they're huge - we're talking one story house sized in some cases, and much bigger than a car.
With megaclasts like these, the question related to both wave height and force, because not only did there need enough force to rip them out, a certain amount of force, or speed, is also necessary to create and maintain what's called "suspension velocity" even if the boulders were just bouncing along and not completed suspended. The calculations they came up with equals a wave height between the bounds of 170 m and 270 m.
So: not only do they have evidence and age dating of a collapse event of the volcano flank, they have evidence and age dating that correlates to that collapse of a tsunami on a nearby island, and not just a tsunami but one 170+m. IMHO that's some outstanding science, particularly with the building on other pieces of research and evidence.
One of the laws of geology is that the present is the key to the past. But it's also true in reverse - the past is the key to the present. Geology is not just past events - geology is now. There's some discussion about whether or not certain kinds of landslides can generate megatsunamis, and here is evidence of just that in the geologic record. There are probably other examples out there, but it could, for various reasons, be extremely hard to preserve; here is a circumstance where it was. We should learn from it.
posted by barchan at 8:56 AM on October 5, 2015 [13 favorites]
The point of the actual study (to which I have access) was to prove that the boulders are indeed tsunamigenic, or deposited from a tsunami; that dating of the deposits would fit the dating of the collapsed flank of the volcano; and then to calculate wave height and energy to to show that giant, collapse generated tsunamis do exist in the geologic record. Below the boulders in the valleys and slopes are run-up sheets of sand which thin up-slope; chaotic conglomerates and other boulder deposits, and rip-up clasts of various types. Additionally there is the cliff band of basalt, which was a submarine (under sea) lava flow which produces a basalt with a very distinctive joint pattern; dating of the basalt itself showed an origin of ~2.5-2.3 m.y.a., and it was then uplifted. (Part of the study has to deal with how much of the island has been uplifted and when to properly calculate wave height.) Essentially the boulders on top of the plateau are giant rip up clasts where the wave tore rocks from that cliff band of lava. And they're huge - we're talking one story house sized in some cases, and much bigger than a car.
With megaclasts like these, the question related to both wave height and force, because not only did there need enough force to rip them out, a certain amount of force, or speed, is also necessary to create and maintain what's called "suspension velocity" even if the boulders were just bouncing along and not completed suspended. The calculations they came up with equals a wave height between the bounds of 170 m and 270 m.
So: not only do they have evidence and age dating of a collapse event of the volcano flank, they have evidence and age dating that correlates to that collapse of a tsunami on a nearby island, and not just a tsunami but one 170+m. IMHO that's some outstanding science, particularly with the building on other pieces of research and evidence.
One of the laws of geology is that the present is the key to the past. But it's also true in reverse - the past is the key to the present. Geology is not just past events - geology is now. There's some discussion about whether or not certain kinds of landslides can generate megatsunamis, and here is evidence of just that in the geologic record. There are probably other examples out there, but it could, for various reasons, be extremely hard to preserve; here is a circumstance where it was. We should learn from it.
posted by barchan at 8:56 AM on October 5, 2015 [13 favorites]
it's unlikely that a landslide on that scale would be fast and coherent.
Unless we really tick of BLUE HADES.
posted by chimaera at 9:59 AM on October 5, 2015
Unless we really tick of BLUE HADES.
posted by chimaera at 9:59 AM on October 5, 2015
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posted by oheso at 4:55 AM on October 5, 2015