Question for OTF's geologists

[Rogin the Armchair fan]

I get the idea of tectonic plate movement, and how two lumps of rock crunching up against each other along a fault line will eventually release all that pressure in a massive earthquake like the one in Szechaun yesterday.

And, indeed, over millions of years, and hundreds of thousands of similar earthquakes that lift the ground by 2m at a time, throw up huge mountains like the Himalayas.

But - two questions - why do all the major earthquakes that are reported nowadays seem to happen in densely-populated areas that aren't in mountain ranges? Is it just that it's only that it's because the earthquakes that cause massive devastation to human populations are reported, whereas one that are still occurring in regions like the Himalayas (which by all accounts are still "growing") go unreported?

And secondly, are all mountain ranges the result of this kind of plate activity? If so, what about, say, the Pennines, in England? I thought we were miles away from the nearest "fault line" - I think it's now in Iceland - how do those mountains end up in the middle of a plate, away from where they were "born"?

[Femme Folle]

Question for OTF's geologists

If an earthquake happened in the middle of nowhere, would anyone be there to report it?

Aren't tsunamis caused by earthquakes under the sea?

[Incandenza]

Question for OTF's geologists

Rogin the Armchair Fan wrote:

But - two questions - why do all the major earthquakes that are reported nowadays seem to happen in densely-populated areas that aren't in mountain ranges?

What other ones are you talking about?

Not all faults are in mountain ranges.

[Ginger Yellow]

Question for OTF's geologists

Um, you do remember the massive earthquake in Kashmir, right?

Not all mountains are formed by crashing plates. Mantle plumes can create mountain chains as plates pass over them (eg Hawaii).

I'm not sure on the geological history of the Pennines, but bear in mind that the current layout of the plates is nothing like what it was millions of years ago.

[Rogin the Armchair fan]

Question for OTF's geologists

the current layout of the plates is nothing like what it was millions of years ago.

So how does that happen? If you've had something at a fault line that has thrown up mountains (in the past) because of plates crashing together, how do they just "stop" and leave a mountain range in the middle of an area of relative geological inactivity, like the middle of Britain?

Do some fault lines just "heal over", and does anyone know how, or why?

[caja-dglh]

Question for OTF's geologists

The Pennine range is mostly as a result of the ice age, glaciation and the process of forming cut aways. Nothing volcanic about it all, best I know, just hill ranges that became more defined through the process of glaciation.

Ice forms on hills, as the temperature rises it starts to loosen and moves and cuts away profiles defining it as more mountainous. Hence the great collection of truncated spurs, corrie lakes and all other things I learned in the Ice Age class in Geography over fifteen years ago.

The Alps aren't particularly dissimilar I would hazard a guess. The only major volcano I know in the UK is in Edinburgh, and the profile of rock there is hugely different.

[evilC]

Question for OTF's geologists

Aren't the Alps formed by Italy (or, rather, the plate that it is on) slowly crashing into Southern Europe? Plently of volcanoes, earthquakes etc in Italy, obviously.

(Is the Med on its own mini-plate or is it on the same plate as Africa? I'll have to run off and look that up soon.)

Aberdeen is made up almost entirely of Granite - that's a result of that Edinburgh volcano, isn't it? ...Or was it a separate volcano in its own right? Both extinct now, of course.

[Anton Gramscescu]

Question for OTF's geologists

If you've had something at a fault line that has thrown up mountains (in the past) because of plates crashing together, how do they just "stop" and leave a mountain range in the middle of an area of relative geological inactivity, like the middle of Britain?

Do some fault lines just "heal over", and does anyone know how, or why?

I dunno about the Pennines specifically, but mountain ranges thrown up by plates crashing into each other do erode over time. The Appalachians and other mountain ranges down the east coast of North America used to be a lot taller than they are now. So too did most of the Alps, Rockies and Himalayas. The Andes are, I believe, the newest range, and peaks there are noticeably sharper and craggier as a result.

Fault lines are not necessarily *in* mountain ranges, but they're usually not far from them, either. California's San Andreas fault, for instance, is not in the mountains but was created by the same process that threw up the Rockies and other mountain ranges along the west coast of North America.

The Alps were created by Africa running into Europe (as Clive suggests, much of the mediterannean is on the African plate). Glaciation had nothing to do with their creation, though certain specific features like Alpine lakes are the product of the most recent ice ages.

[Carcass]

Question for OTF's geologists

The process by which mountains end up away from fault lines is known as continental drift. The Mid Atlantic Ridge is where new land is being created continuously pushing the land masses at either side of it in an outward direction.

You also get plates colliding together where one slides under the other. It's not all just plates slamming into each other.

In fact in the case of the San Andreas fault which runs through California, it's a case of one plate being pushed in a notherly direction while the other's being pushed south.

[anton pulisov]

Question for OTF's geologists

If you've had something at a fault line that has thrown up mountains (in the past) because of plates crashing together, how do they just "stop" and leave a mountain range in the middle of an area of relative geological inactivity, like the middle of Britain?

Europe used to be mashed up against America 400 million years ago, which resulted in very tall mountain range similar to what the Himilayas are like now. As somebody said, the Highlands of Scotland and the Appalachian Mountains were essentially a part of the same mountain building process. Then, when Europe and America drifted apart (forming the Atlantic Ocean), the mountains slowly became weathered away to what they are now, impressive hills, but nothing on an Everest scale. They are really ancient hills though, the Highlands of Scotland contain some of the oldest surface rocks on the planet.

Another interesting mountain range where you wouldn't expect to find one is the Ural mountains, which were created when Europe and Asia bashed into one another. They have since been weathered down to a smaller size, just as the Himalayas will be in the future.

Future developments will see the Mediterranean Sea closed in and the Alps become as high as the Himalayas are today.

[San Bernardhinault]

Question for OTF's geologists

I think you tend to get more earthquakes in subduction zones, where one plate is moving under another and you get occasional slips, than in uplift areas where plates push into one another. But you do get tons of earthquakes in mountainous regions.

I think that eventually plates merge/meld into one another when they combine, and chunks break off to form new plates. Which is why you can end up with old mountains (like the Pennines or Appalachians) which have eroded down, and which are no longer near "real" fault lines. There's usually still a smallish fault in the plates around those areas, but they're all largely moving together as part of the larger plate. You still get earthquakes along those partial faults, but they tend to be more infrequent and smaller.

[Bill Poster]

Question for OTF's geologists

I don't understand Geology.

Whose fault is that eh?