Model Setup:
picture 5: Model set up gelatin tank
To simulate magma dikes propagating through
the Earth's crust to a volcanic load we use gelatin and air dikes
propagating to a load placed on top of the gelatin. The tank used
is a six gallon plastic tank. It has had holes drilled in the
bottom. There are eleven holes one in the middle and five
reaching out on both sides spaced in five centimeter intervals.
The holes are used to project the air dikes into the gelatin. The
air dikes are projected using a 50ml syringe with a needle screwed on
to the end. There is 20ml of air injected into the gelatin.
The tank is a six
gallon tank filled with five gallons of gelatin, the gelatin reaches
17.2cm on the 21cm tank, and it is made from five gallons of water with
700ml of the gelatin mix dissolved into it, the gelatin used was
standard Knox unflavored gelatin. The load is applied
by a plastic sheet that is 17.5cm by 12.7cm and weighs 300g, and placed
on top of that is a rock slab which weighs 325g.
Experimental Observations:
During the experiment we see that the dikes propagate to the edges of the load on the surface. This happens because the maximum compressive stress in the system is at the edges of the load and not in the center. The air dike propagated up the center of the tank shows how a dike would act when there was no load and the maximum compressive stress was right above where the dike was begining to propagate. (watch the video) At any other point at the bottom of the tank the compressive stress would be at its max in a direction towards the load.
Experimental Observations:
During the experiment we see that the dikes propagate to the edges of the load on the surface. This happens because the maximum compressive stress in the system is at the edges of the load and not in the center. The air dike propagated up the center of the tank shows how a dike would act when there was no load and the maximum compressive stress was right above where the dike was begining to propagate. (watch the video) At any other point at the bottom of the tank the compressive stress would be at its max in a direction towards the load.
The maximum compressive stress is in the center of the tank while the
vectors get further apart as they get further away from the load.
These vectors show lines of same stress in the gelatin. As they
move away from the load they get further apart because the further the
gelatin is from the load the smaller the compressive stress from the
load
is. If the dike propagates far enough away from the load it
will not be affected. Also There is a point where the load does
affect the dike but not enough to move it all the way to the load. (watch the video)
In the figure the arrows are the direction of the maximum compressive
stress, you can see that the compressive stress is not always straigh
down.
The equation used to find the magnitude of the compressive
stress
from the load at any point at the bottom of the tank is:
C=mg*SinΘ (Walker, 2007)
Where C is the quantity of the compressive stress that reaches a particular point on the bottom of the tank, m is the mass of the load, g is the gravity constant and Θ is equal to the angle between the bottom of the tank and a line from the begining of the dike to the load.
C=mg*SinΘ (Walker, 2007)
Where C is the quantity of the compressive stress that reaches a particular point on the bottom of the tank, m is the mass of the load, g is the gravity constant and Θ is equal to the angle between the bottom of the tank and a line from the begining of the dike to the load.
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Table 1: Data table showing the actual force and percent of the force from the load at certain points at the bottom of the tank. |
In this data we see that the force from the load decreases as we move away from the center of the tank. We also see that the dike propagated from the furthest out point was affected by the load very little. The dike curves slightly towards the load but in a much smaller quantity than dikes propagated closer to the load. We also see that the further the dike is from the load the slower the dike propagates towards the surface, and that as the dike propagates higher in the gelatin the dike slows down and sometimes needed more air to be added for the dike to reach the surface.
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