Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: Pseudoscience-is-malarkey on 10/06/2021 00:59:50
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Are there mountains we know of that once flourished the surface of the Earth, but have since disappeared?
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Yes. Look for any areas with granite.
Granite is thought to form as crustal rocks melted and slowly cooled, deep beneath mountain ranges.
- If granite is now on the surface, then the mountain range has eroded away.
See: https://en.wikipedia.org/wiki/Granite#Origin
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Yes. Look for any areas with granite.
Most of Cornwall, UK
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Following on from the OP's question, if there were mountains, in past ages, which exceeded the height of our present-day highest mountain, Everest - could geologists find enough evidence to find them, and deduce their height?
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Following on from the OP's question, if there were mountains, in past ages, which exceeded the height of our present-day highest mountain, Everest - could geologists find enough evidence to find them, and deduce their height?
That sounds tricky, but it might just be possible. If they can deduce the average rate of mountain growth due to plate tectonics in a given area at a given period of history and compare that with predicted erosion rates over the same time period, they could potentially model what the maximum allowed height for a mountain could have been. There are also limits placed upon a mountain by the laws of physics. If it's too tall, the pressure at the bottom of the mountain will overcome the compressive strength of the rock. Alternatively, it can also cause the crust in the area to become depressed, lowering the height of the mountain above sea level.
Given that the Earth's interior cools over time, the internal temperature (and thus plate tectonics and subsequently average mountain growth rates) should have been higher in the past.
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You might also be able to get some information about how fast the rock cooled from the size of the crystals and the cooling rate is influenced by the size of the rock.
But, obviously, that would involve mathematics so Charles won't pay it any attention.
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If (a mountain is) too tall, the pressure at the bottom of the mountain will ... cause the crust in the area to become depressed, lowering the height of the mountain above sea level.
In fact, mountains are like floating icebergs - most of their mass is below, rather than above the surrounding surface...
- Crustal rock is about 85% of the density of the underlying mantle rock, so you could guess that the mountains would be about 5 times deeper below the crust than they are above the crust (if it were in equilibrium, which it never is...)
- This mountain flotation is called "isostasy"
See: https://en.wikipedia.org/wiki/Isostasy#Deposition_and_erosion
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There are many volcanic mountains that have gotten shorter over the ages.
Mount Tambora (https://en.wikipedia.org/wiki/Mount_Tambora) was estimated to be 4,300 meters (14,100 ft) prior to 1816, and 2,850 metres (9,350 feet) after 1816.
Around here, Mount Mazama (https://en.wikipedia.org/wiki/Mount_Mazama), as well as Mount Saint Helens (https://en.wikipedia.org/wiki/Mount_St._Helens) have lost their tops.
There is some speculation that the Island of Santorini was Atlantis prior to an eruption leaving a sea level caldera (https://en.wikipedia.org/wiki/Minoan_eruption), as well as devastating parts of the island that remained above water.
(https://upload.wikimedia.org/wikipedia/commons/thumb/1/14/Santorini_Landsat.jpg/465px-Santorini_Landsat.jpg)
Although, it may have already been a caldera + cone prior to the most recent eruption.
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Other mountain removal techniques are available.
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It might take some hunting, but inevitably at least some of the large asteroid impact events have completely destroyed hills or mountains.
It might be hard to discern what was under the impact crater unless it hit the middle of a mountain range.
According to this article, the Chicxulub impact may have momentarily pushed up a mountain higher than Mt Everest, (https://www.bbc.com/news/science-environment-38019604)but it rapidly collapsed back down as part of the event.
The Vredefort crater (https://en.wikipedia.org/wiki/Vredefort_crater) is about 2 billion years old, and largely eroded away. Core samples may show characteristic layers of earth displaced by the impact.
Other large craters (and domes/rings) may be even more difficult to discern.
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if there were mountains, in past ages, which exceeded the height of our present-day highest mountain, Everest
There is one, today - in Hawaii.
Hawaii's Mauna Kea volcano rises 4.2 km above sea level, but 10.2km above the surrounding sea floor.
Everest is 8.8km above sea level, but only 3.6km above the adjacent Tibetan Plateau.
Earth's rotation gives Chile's Chimborazo a boost...
See: https://en.wikipedia.org/wiki/Mount_Everest#Comparisons
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Most of Cornwall, UK
Most of all of Cornwall budy!