Naked Science Forum

Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: on 03/11/2007 21:40:32

Title: Maximum height of mountains
Post by: on 03/11/2007 21:40:32
is there one, or can they just keep getting higher and higher...?
Title: Re: Maximum height of mountains
Post by: another_someone on 03/11/2007 23:54:44
Higher than what?

Most mountains are measured in height against sea level, but ofcourse sea level can drop, so then all mountains can get higher.

There are several matters that I can imagine could effect mountain height.

In the long term, erosion will limit mountain height, but that is not a short term issue.

Obviously, if you want to raise a lot of rock to great altitude, you need energy from somewhere to do it.  Mostly this comes from heat from the Earth's core, so the limiting factors here are both the total amount of energy available from that source, but more pertinently, how much of that energy can be concentrated in a small enough area to raise rocks to a desired height.

There will also be a limit on the steepness at which a mountain side can ascend without crumbling, but that simply means to to gain a certain height, you need to raise more material to half that height to support the lesser material to the full height, and this comes back to the energy available to do this.

While I am talking of energy, what is probably more important is power (the amount of energy available over a specific period of time) rather than overall energy, since if the available power is too small, then even if the overall energy available is sufficient, the rate of mountain building would be slower that the rate of erosion that is reducing the mountain size.
Title: Re: Maximum height of mountains
Post by: daveshorts on 04/11/2007 11:30:38
On earth one of the biggest limiting factors is erosion the higher the mountain the more energy that can be released by rolling a rock down it, so the faster they will roll down so if the mountain isn't being built as fast as it is being eroded it won't be growing.

Really big mountains are created when two tectonic plates collide and the biggest ones when two continental tectonic plates (the ones that are made out of lighter rocks and make up the land) the continental plates are dragged around by the oceanic plates getting cold and sinking into the mantle. India is attached to a piece of  oceanic plate that has been subducted and is dragging India into Asia building the Himalayas. Of course the problem is that as soon as the two continental plates collide you start to run out of oceanic plate to pull them together, so this limits the total amount of energy that can go into mountain building.

The other effect that limits it is that the plates are floating on the mantle and if you want to build a mountain you have to make the plate thicker so it floats, mountains are a bit like icebergs they have much more (could even be about ten times more) root than actual mountain so a much bigger plate collision will only give you a slightly bigger mountain range.

So in the present conditions of the earth you could probably build a higher mountain than everest but I doubt that it could be twice as high.
Title: maximum height of mountains
Post by: Alandriel on 04/11/2007 20:49:43
Very interesting answers! [:)]

Talking of 'the highest mountains' I just recently came across:

Olympus Mons, a huge mountain on Mars, is the largest mountain in our Solar System (so far).
At its highest point Olympus Mons is over 69,800 feet (just over 13 miles) tall.
In comparison, Mount Everest is 'only' 29,028 feet (about 5 and a half miles) high.

No erosion per se on Mars and no tectonic plates [;D]

Title: maximum height of mountains
Post by: another_someone on 04/11/2007 23:25:22
There is erosion on Mars, but not water erosion, and atmospheric erosion is in a less dense atmosphere.

More critically, the mass of, and thus the gravity on, Mars is only 10% of that on Earth, and thus the amount of energy required to raise an object to a given height on Mars is only 10% of the energy required to raise a similar object to the same height on Earth.

On the other hand, that is why I asked what you are measuring the height from.

Olympus Mons is 69,800 feet above the average surface height of Mars, whereas Mount Everest is measured from sea level.

Although it still leaves Olympus Mons to be higher than Everest even in comparable measure, since the deepest point in the oceans are still only 35,840 feet below sea level, so Everest is only 64868 feet above the lowest point on the Earth, and its height above the average height of the Earth would be somewhat less than that.
Title: maximum height of mountains
Post by: JimBob on 05/11/2007 04:09:57
Well, probably time a geologist got involved in this. There is no limit practical limit to the height of mountains on earth. The highest mountain is not Mount Everest. Mauna Kea in Hawaii is over 10,000 meters above it's base. That is how I would define a mountain. And no, water has nothing to do with it.

Water is also active on Mars. It can be seen in the side of some of the valleys eroding slightly the sides of them as it melts. This happens only near the equatorial areas of Mars but there is water seeping out of (most likely) sandstones. The Himalayas are still being thrust upward and could potentially be almost as large as those on Mars. It has probably happened in earth's history.  I know that the analysis of the widths of the roots of the Appalachians in Pennsylvania and New York state indicate that they were much taller than the Himalayas are now.

The Himalayas are young and still very active. The Indian Plate collided with the Asia Plate about 60 million years ago. Present growth rate is at least 5 millimeter per year. Over a million years that is a HUGE amount of growth - 5000 meters. If it continues only 6 million more years that is another 30,000 METERS, not feet.

Yes, erosion takes place but the higher the mountains are, the less weather there is and, thus, less erosion.