Sunday, February 17, 2008

More on delta sinking

This article didn't make a spick of sense to me, but maybe it does to others...

They said that people thought the subsidence was in the deep rock. Who the heck thought that? The Army? They come to the conclusion that the consolidation is in the soft muck at the surface. Ya think?

I really like the comment that this is a good thing, since you can anchor structures 300 feet down!

I love articles like these!


BrianR said...

You might be referring to this statement:

"The prevailing theory up to now has been that subsidence occurs deeper beneath the surface in Earth's crust due to the crushing weight of accumulating sediment."

This is another example of mis-reporting ... what they are talking about is much deeper subsidence, but not really in the "crust" ... the column of deltaic material is km thick. So, yes, there is indeed "deep" subsidence related to large-scale growth faults and such ... but, the quicker subsidence, as they say in the article, is the uppermost and least compacted stuff.

Unfortunately, the researchers did not do a good job of explaining this to the reporter, the reporter didn't listen/understand, or probably a combination of both.

Harbles said...

Caught between the 'Rock' of reduced silt deposition due to navigational and flood control 'engineering' (I use the term politely) upstream and the 'hard place' of rising sea levels due to global climatic change I dare say the Big Easy has more of the miseries commin' and the Army Engineers have neither the competence or resources to do a thing about it.

I would think the bedrock would be rising due to reduced silt load?

Harold Asmis said...

My impression was that if you were to invoke the mechanism of deep subsidence, it would be crustal subsidence as with the east coast. This is due to general cooling and is probably 1-2 cm per century. Soft soil consolidation (the squeezing out of water) is always most rapid with the new upper loon shit.

Nevertheless, I can't see the Army using 300 foot piles sometimes soon!

BrianR said...

Yeah, there's the thermal subsidence that is typical of rifted margins, which would be crustal, but there's also large-scale gravity-induced subsidence of thick sedimentary columns along margins ... and then, of course, the de-watering/compaction of the uppermost fluffy stuff ... quantifying the relative contributions is the tough part.