re: Now Closed: Everything you ever wanted to know about EARTHQUAKES

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Also, have you ever been in an earthquake? They are so fricking scary!

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Yep. I still jump and squeal like a little girl every time one hits. You'd think I'd be used to it after 5 years of feeling them all the time...nope.

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quote: What's the seismic activity we (S. LA folks) need to be most concerned about?

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When LF scores with .01 on the clock to beat Bama is the next activity we will feel.

Wow, you had to dig deep for that one.

Do you have the one sans swoop?

Dude, your Rag avi is throwing me the hell off. I keep thinking rag is back.

How to survive one?

Ha!!!!!

Boom

I knew north and South America were colliding with each other.

South America use to have a whole bunch of flightless birds until the mammals of North America killed them all out after the 2 continents were connected by the newly formed Central America form by the collusion of the north and South American plates.

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Hundreds of thousands of pounds of sediment wash off the surface of the US and down the Mississippi River each year, but the elevation of the Mississippi River basin is relatively unchanged. Why aren't we slowly eroding down through the crust? What replaces the lost topsoil?

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Excellent question!

In simplest terms you're asking: Why don't rivers carve all the way through Earth?

First, you need to understand the thickness of the crust. Continental crust is 50 kilometers thick on average. A feature that occurs on the surface won't ever be able to reach that far down.



The next part of your question deals with the removal of sediment to the point where there is no sediment left. Any time sediment is removed from an area is called erosion. But let's talk excessive amounts of erosion, like combining all the major rivers into one. What would happen?

That's pretty easy to figure out. The Earth, at great depths is divided into layers. The crust, where rivers work, lies above the mantle. The mantle is part liquid and more dense (3.3 g/cm3) than crust (2.7 g/cm3), which allows crust to actually sink into the mantle but still stay afloat. I bring this up because the level to which crust sinks into the mantle deals with the thickness of the continental crust.



So, let's say you have a mountain. If you have our super river that has the sole purpose of eroding that mountain, then the crust under the place that mountain once was would be thinner than it used to be. This would make the mantle want to push up through the crust there because the crust isn't as thick there. In doing so, this will cause the land to bulge up.


You can see it here when a glacier is removed from the crust after, say, an ice age.

So what I'm saying is, the mountain would remain there if you could make the crust rebound fast enough. This process of the equilibrium between crust and mantle is called isostasy.


white perch for joxy

pretty damn interesting thread here, pectus....

have you ever cleaned all of the topsoil away and seen an actual fault?...I am talking about the actual two pieces of rock that would move relative to one another?....

if so, I would have to do some kind of permanent marking of the two pieces of rock, so I could see the movement over time...maybe take a photo of it every year over my life or something cool like that...

Is there a fault in Natchez, MS? Why is it so high on a bluff compared to other Mississippi River cities?

The town of Natchez sits on loess bluffs. Loess is silty and often makes cliffs if scraped by rivers due to erosion. It is fairly easy to erode.

Natchez is high because it is on the outside of a turn in a river, which is known as a cut bank. The other side of the river is levelled due to the river removing all the loess. In a few thosand years, Natchez will be levelled as that bend in the river migrates further east as it keeps cutting into the loess cliffs.