# The Naked Scientists Forum

### Author Topic: What governs the height of a mountain on Earth?  (Read 9726 times)

#### Evgeniy Podolskiy

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##### What governs the height of a mountain on Earth?
« on: 03/03/2009 11:30:02 »
Evgeniy Podolskiy  asked the Naked Scientists:

When I was graduating from the university Mt. Everest was claimed
to be 8848 m high, now new measurements show that it is 8852 m.

So I am just wondering- how high actually any mountain on Earth can be? Can some peak reach 20 km like Olympus volcano on Mars or there some physical geological limit exists determining the maximum height (like underlying geology, pressure in the mantle and etc.)?

And also another related thing: were there any mountains higher than Everest in the Earth history?

What do you think?

#### Supercryptid

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##### What governs the height of a mountain on Earth?
« Reply #1 on: 04/03/2009 04:41:30 »
Gravity would be one limiting factor in the size of a mountain. If a mountain gets too large, the pressure at the base of the mountain will become so great that it will overcome the compressive strength of the rock. Rocks can only handle so much pressure before failing. This may be one reason why Olympus Mons on Mars is so much larger than Mount Everest on Earth. The significantly reduced gravity there allows more mass to be piled up on the base rocks before they are crushed.

#### blakestyger

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##### What governs the height of a mountain on Earth?
« Reply #2 on: 04/03/2009 10:02:40 »
Yes - and Martian landforms are no longer subject to erosive forces.

#### Bored chemist

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##### What governs the height of a mountain on Earth?
« Reply #3 on: 04/03/2009 18:59:05 »
Mountains are thinner at the top than at the base so there's more rock there to hold them up than weight at the top pressing them down. If they get thinner faster than they get taller there's no problem holding up the weight. There might be a theoretical limit but I think it's when the gravity pulling in all directions makes the thing into a sphere.
Of course erosion would be the real limiting factor here.

#### LeeE

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##### What governs the height of a mountain on Earth?
« Reply #4 on: 04/03/2009 20:40:17 »
Mt. Everest/Chomolungma, raised by the impact of India in to the Asian continent, is actually still growing in height.  The very top portion of the mountain is largely limestone and contains fossilised bits of trilobites, crinoids, and ostracods, showing that it was once part of the sea floor.

#### JimBob

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##### What governs the height of a mountain on Earth?
« Reply #5 on: 06/03/2009 04:30:30 »
The theory of istostacy states that the earth's crust will, in general, act as a fluid, with excess weight causing an "Iceberg" effect on the crust, the heavier the substance the greater the depth to the beginning of the  mantle under the crust. But this is rarely the dominant mechanism acing on the structures of the earth. (An exception would be the weight of ice deforming the crust during the height of the Ice Ages.) Rocks, even the hardest one, act as an elastic "solid" under stress - both compressional and extensional stresses.

Thus, depending on the combined characteristics of the rocks forming the crust at any given place on earth - the elastic properties of the rock, comprised of the bulk modulus, shear modulus, & Young's Modulus, as well as the compressional strain and the shear strain - all these variables must be taken into consideration to describe the projected behavior of any one geologic province under consideration.

In the particular case of the Himalayas, the confining compressional stress of the crust is the dominant force presently acting on these mountains. The compression is due to the Indian Plate colliding with the Asian Plate.

The Indian plate is continuously moving north about 2 cms a year. As a result, the Himalayas are rising at about 5 millimeter per year. It is calculated that this may well continue to rise above 40,000 feet ABOVE seal level.

Mauna Kea volcano in Hawaii is the tallest mountain on earth at 33,476 feet above it's base. Mauna Loa, the largest volcano on earth, is only 120 feet lower that Mauna Kea.

Now, consider that the Challenger Deep in Marianas Trench is 35,798 feet below sea level. Thus, there is a total relief of the earth's crust of  29,041 + 35,798 = 64839 feet or 12.28 miles.

There are also other facts to be consider, making the claim of Everest being the highest mountain true only in one sense.

FROM WIKIPEDIA:
http://en.wikipedia.org/wiki/Mount_Everest

"Everest is the mountain whose summit attains the greatest distance above sea level. Several other mountains are sometimes claimed as alternative "tallest mountains on Earth". Mauna Kea in Hawaii is tallest when measured from its base;[25] it rises over 10,200 m (6.3 mi) when measured from its base on the mid-ocean floor, but only attains 4,205 m (13,796 ft) above sea level.

By the same measure of base to summit, Mount McKinley, in Alaska, is also taller than Everest. Despite its height above sea level of only 6,193.6 m (20,320 ft), Mount McKinley sits atop a sloping plain with elevations from 300-900 m (1,000-3,000 ft), yielding a height above base in the range of 5,300-5,900 m (17,300-19,300 ft); a commonly quoted figure is 5,600 m (18,400 ft).[26] By comparison, reasonable base elevations for Everest range from 4,200 m (13,800 ft) on the south side to 5,200 m (17,100 ft) on the Tibetan Plateau, yielding a height above base in the range of 3,650 m (12,000 ft) to 4,650 m (15,300 ft).[21]

The summit of Chimborazo in Ecuador is 2,168 m (7,113 ft) farther from the Earth's centre (6,384.4 km or 3,967.1 mi) than that of Everest (6,382.3 km or 3,965.8 mi), because the Earth bulges at the Equator. However, Chimborazo attains a height of only 6,267 m (20,561 ft) above sea level, and by this criterion it is not even the highest peak of the Andes."

SO,

There is a lot more to the matter than just gravity.

(As I am back and have worked the last 5 days, tomorrow, Friday is going to be a "down day" (if the phone doesn't ring) so I will see if I can find the theoretical highest possible mountain on planet earth. This calculation WILL take gravity into consideration. I am rather sure it is about 40,000 feet above sea level or above its base, as stated above BUT I want to be sure.)

#### The Naked Scientists Forum

##### What governs the height of a mountain on Earth?
« Reply #5 on: 06/03/2009 04:30:30 »