|How tall was Mt. Everest before wind erosion and
water erosion happened?
Well, it is a little more complicated because as
Mt Everest grew, that is, as the land went higher
and higher, at the same time erosion was taking
place. So the actual height at any time is the
balance between the uplift rate vs the
degradation rate by ice, water and mass wastage.
So, here is a nice way to think about it:
Let’s say you start to fill your bathtub but the
valve at the bottom leaks a little. Then when you
turn the water on the amount of water in the tub
will begin to increase, but there is a leak!!! So,
if the leak rate is less than the fill rate, the
tub WILL accumulate water, but if the leak rate is
greater than the fill rate, well the tub will be
EMPTY, no matter how long you run the water!
So, the height as a function of geologic time
of Mt Everest is the difference between the rate
of uplift vs the rate of erosion.
What drives the uplift?
We know that gravity, wind, water, ice, and mass
wastage drives the leak. But what drives the input
Uplift is driven by the collision of INDIA
with ASIA. These two continents are on
separate plates (plate tectonics) and when the
plates collide, the stuff has NO WHERE TO GO... so
it goes up! Then gravity works against that.
Fantastic question! Mountain don't get pushed up
all at once, and then simply begin to erode.
Rather, mountains are uplifted and worn away
simultaneously. If uplift exceeds the rate of
erosion, a mountains slowly gets taller through
time. Conversely, if erosion rates are higher
than the rate of uplift, mountains become
lower. So...Mount Everest continues to get
pushed up (since the Indian Plate is continuing
its collision with the Asian Plate), but, as you
note, wind and water (not to mention gravity,
chemical weathering, plus other factors) are
working to lower it. Nobody knows how high Mount
Everest might have been in the past, but there are
good theoretical reasons to think that it was
never much higher than it is today. One factor to
consider is that the bigger and heavier Mount
Everest becomes, the more it's root sinks into the
less solid interior of Earth. A good analogy is
stacking bricks onto a trampoline. The more bricks
you stack onto a trampoline, the further that pile
of brick that you're building sinks into the
trampoline. With time, the top of brick pile
doesn't necessarily get higher as you continue to
add bricks, because as the weight of the pile goes
up, so does the amount of sagging.
Bottom line--the height (and shape) of
mountains reflect the relative rates of uplift and
erosion--the elevation of mountains is never
steady over geologically significant spans of
Mt. Everest is actually growing and not
eroding! As tectonic plates push together, it
pushes the mountain up higher than even before.
Erosion happens so slowly that Mt. Everest is
actually still getting higher rather than shorter.
Mt. Everest (and any other mountain) is in a
constant battle between erosion and geological
uplift that creates mountains in the first place.
The uplift is still pushing the mountain up as
erosion bring it down. There are also faults that
the different rock formations that make up the
mountain can slide past each-other along. I do not
know which of these forces is currently winning,
if Mt. Everest is getting shorter, or if it is
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