Roger Weller, geology instructor email@example.com
last edited: 7/8/15
Water on Mars...Catastrophic
Collapse and Floods
In the following photograph of the surface of Mars, there can be no other explanation other than the following: Support was removed from beneath a brittle layer which then collapsed and broke into many pieces. Next to the collapsed area is a large flow structure along which major erosion has occurred. The two features are linked together. A very large quantity of fluid must have suddenly drained out from beneath the overlying brittle crust.
There are only two types of
fluids that can be used to explain flow features on Mars: lava and water. Lava
is unlikely because of the wide, shallow nature of the flow channel. Water or
water mixed with Martian soil is a better explanation. The width of the flow
channel and the large extent of the collapsed surface imply that there was a
very large quantity of fluid that drained from beneath the brittle crust.
Where did all of this fluid come from?
As discussed in the first
two experiments, water in liquid form has a very difficult time existing in the
thin Martian atmosphere. Water just above the freezing point would just boil
away to form water vapor. A large quantity of water would take longer to boil
away, so a large flow of water suddenly released at the surface could exist long
enough to flow many miles.
But we still face the problem of how could so much water accumulate beneath the surface without it boiling away. If water is under pressure, the temperature at which it boils is increased. On Earth at sea level atmospheric pressure is about 15 pounds per square inch and water boils at 95 degrees Celsius (212 degrees Fahrenheit). At an elevation of 2 kilometers above sea level (about 6500 feet) air pressure is less at water boils at 93 degrees Celsius. If water could be kept under pressure beneath the Martian surface, it would not boil away.
Close examination of the broken and down dropped surface indicates that the brittle layer was quite thick, perhaps as much as 300 feet. The weight of the overlying layer could have provided the pressure on the underlying water. This weight acting on the water is called Lithostatic Pressure. On Earth a layer of rock 300 feet thick would create a lithostatic pressure of about 300 hundred pounds per square inch. On Mars gravity is only one third of Earth's gravity and so this layer would create a pressure of 100 pounds per square inch. A pressure this great would easily keep water from boiling away.
Water under the ground is
groundwater. As discussed in the two previous experiments regarding porosity,
the water must occur in the open spaces between rock and silt fragments. In
other words, the groundwater is mixed in with sediment. The fluid that drained
out quickly from beneath the overlying brittle crust would have to be something
like mud, not pure water. Mud normally does not flow very quickly. If the mud
layer was exposed quickly by a meteorite impact or a Mars quake, the lithostatic
pressure would disappear and the water in the mud would start to boil
The material that violently and suddenly flowed out from beneath the brittle crust was probably a mixture of silt, rock fragments, water, and lots of expanding bubbles of water vapor!
There is still one more
problem to deal with. The surface temperature on Mars is so cold that water
should be in the form of ice. Beneath the surface, the groundwater and sediment
should be frozen together as permafrost. Where did the heat come from to melt
the permafrost? There are no surface features in the area that indicate
volcanism. However, there could be bodies of hot magma beneath the surface
called igneous intrusions that could be the source of the heat.
Without collecting samples
to date the event, we cannot tell when this massive eruption of mud and water
vapor took place.
CATASTROPHIC FLOW EXPERIMENT
Using the sandbox let's try to see if we can duplicate some of the features seen in the Martian photographs.
1. First, fill a gallon-size zip-lock plastic bag with water. Try not to leave any air in the bag.
2. Next, create a long low slope of wet sand in the sandbox.
3. At the top of the slope bury the plastic bag of water so that one corner of the bag slightly sticks out of the slope.
4. Cover the bag with about one inch
of wet sand. The water in the bag sloshes around; so smooth the surface above
the bag so that there are no cracks at the surface.
5. Dust the slope with a very thin
layer of dark dirt. This will help show the flow channel better.
6. With a pair of good scissors, quickly cut off about one inch of the exposed corner of the water-filled plastic bag, setting off the flood and collapse.