When the Mountain Hit the Ground

7/29/2019 When the Mountain Hit the Ground

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When the mountain hit the ground, the rock under it would be damaged, but only a little. The

granite base is strong enough to hold up under the tremendous resting weight of a

mountain;[5] the shockwave from dropping it an inch doesn't add too much pressure on top of

that, and the rock would survive with a little minor cracking.

People nearby would definitely feel the impact, and probably hear it; the sound would likelyresemble the crack of a lightning strike (if you were standing near the mountain) fading into a

long, deep rumble.[6] The vibration would be equivalent to that of a 3.5-magnitude

earthquake[7]; at worst, it would knock a few pictures off the wall if you happened to be living

next to the mountain. Frankly, I'd be more worried about debris flying out of the gap.[8]

Oh. You again.

Ok.

Dropping from a height of one foot wouldn't be all that different.

The mountain would hit the ground at 2.5 m/s, or roughly walking speed. The shockwave from

that impact would be in the range of 50 megapascals of pressure,[9] which granite can handle

without too much trouble.[10][11]


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Ok. Let's jump straight to the end of John-Clark's question:

After falling from summit height to base heightabout 5 kilometersthe mountain would be

moving at roughly the speed of sound.

The last two impacts were pretty minor. This one wouldn't be. The jolt to the ground would be as

violent as in a magnitude 7 earthquake.[12] There wouldn't exactly be a crater, but the mountain

would definitely not be shaped like it used to be. The pressure from the impact would be high

enough to produce some unusual geologic strutures. If you put a lump of coal under the meteor,

the impact would be enough to convert it to diamond (and, unfortunately, smash it to bits). [13]

The good news is that, the last time a magnitude 7+ earthquake hit Denali, no one was

killed.[2] Let's just hope nobody is on the mountain itself when we do this.


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Ok. Last one.

We'd need to lift the mountain out of the atmosphere, out past the orbit of the GPS satellites, to

the very outer limits of the Earth's gravity well. Then we let go.

It would hit Alaska at 10 kilometers per second.

The Last Frontier would not fare well. A 50-mile-wide crater would have obliterated Denali

National Park. Anchorage would be buried under three meters of gravel.[14] The shaking,

combined with the debris falling into the ocean, would cause tsunamis across the Pacific. Across

North America, the ground would tremble. A wind would sweep in from the northwest. The sky

would darken.

In 1815, Mount Tambora erupted in the largest volcanic event in recorded history. The resulting

global veil of aerosols made 1816 the "year without a summer". Snow fell in Massachusetts in

June, ice formed on rivers in Pennsylvania in August, and frost killed most of the spring crops. The

cooling effects lingered for several years.


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The Alaska impact would be far worse. Over the next few months, the skies around the globe fill

with dust. Summer is canceled and winter arrives. Global temperatures would drop by 5 to 20

degrees Celsius and stay that way for a year or more.[15]

On the plus side, we would not be engulfed in a global firestorm. When the Chicxulub comet hit

the Yucatan peninsula 65 million years ago, it blasted molten debris into space. This debris fellback to Earth around the world, heating the atmosphere and igniting global firestorms. These may

have played a role in the mass extinctions.[16]

However, our mountain would carry only about 10% of the energy of the Chicxulub impactor,

which means that it wouldn't be capable of igniting global firestorms.[17] The firestorms would, in

fact, only cover some of North America. So that's a relief.

The northern hemisphere would be covered in ice, but our species would probably manage to limp

through. Civilization, on the other hand, might well collapse. A total collapse of modern civilization

would be a serious blow to the already sluggish economy, and the economic damage could

amount to $80 trillion per year (the total value of all human goods and services). All in all, it would

have serious implications for the upcoming elections.

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When the Mountain Hit the Ground