How Tall Can Mountains Be?

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0:00Olympus Mons, the tallest mountain in our Solar System, towers 21,000 meters above the

0:04surface of Mars -- nearly two and a half times the height of Mount Everest.

0:08On Earth, you would need a spacesuit to survive at that altitude - but could there even be

0:11a mountain that tall here on our home planet?

0:14Based on the strength of Earth's gravity and the density and strength of rock, in principle

0:18you could make a single conical mountain that stretched between New York and Chicago and

0:21soared over 45km!

0:24That's twice the size of Olympus Mons and definitely dwarfs Everest.

0:27However, there are a couple of reasons why we can't actually have that humongous of a

0:30mountain on Earth:

0:32For one, Earth's crust is made up of continental plates that essentially float in the semi-solid

0:37rock of the mantle below.

0:38If you add more weight above the surface, they sink lower into the earth's hot interior,

0:42and when they sink far enough, they soften and basically melt.

0:45For our conical mountain, that gives a new height limit of just 15km.

0:49As well, the powerful collision of two tectonic plates, which creates mountains in the first

0:53place, also fractures and cracks the rock, weakening its structure and exposing it to

0:58erosion.

0:59Over millions of years, freeze-thaw cycles pry at these cracks, while winds claw at the

1:03slopes and streams and glaciers carve deep valleys into the mountainside, all weakening

1:07the mountain's support.

1:08This can end badly.

1:12For example, 3,764m tall Aoraki/Mount Cook in New Zealand had its top fall off one night

1:15in 1991, trimming it down to a 3,754m mountain.

1:20Given all the factors that conspire to limit the height of mountains - sinking into the

1:24earth's mantle, fractures, and erosion - I wouldn't bet on our tallest mountains getting

1:28too much taller than they already are.

1:29Then again, Mount Everest is still growing, 50 years from now, it could be 30 cm taller

1:34than it is today... or it could be a good deal shorter.

1:37We'll just have to wait around to find out.

1:39And, who knows?

1:40Maybe we'll be on Mars by then, anyway.

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