Overview
The applet below ploughs rocks (clasts) trapped in
a glacier bed into a virtual slope of mud (till) until they stick in the
slope (achieve lodgement). At the same time, it calculates
the amount of ice that melts because of pressure on the
rock, the force applied to the rock by the ice, and
the length the clast travels.
This program is a development of that used in
Evans (1998), please see chapter five of
that work for a full explaination, though note the differences outlined below.
For further information, please contact Andy Evans.
Launch applet in new window (may take a short while to appear)
The program runs in two modes. In the first, a single
clast is ploughed into a slope using a given ice speed and
till residual strength. In this mode the characteristics of
the ploughing process are given for each day the ploughing occurs
allowing a picture to be built up, for example, of the amount of
sediment melting out of the ice at each point on the
ploughing gouge.
In the second mode, a ploughing length is given, and various
combinations of ice velocity and till residual strength are
tried to see if they can produce the given ploughing length.
If they can, a set of characteristics for the ploughing
event are given, for example, the total amount of sediment
melted out of the ice.
The applet can also be run as an application. If run
as an application it allows you to specify an output file, which
considerably speeds up runs.
If you run the program as an applet, you can still get results
by using ctrl-x to copy the highlighted results
from the applet.
To run the program as an application, download the file
plough.jar and double-click on it
in whatever file manager you use (e.g. Windows Explorer).
If the program doesn't run, you'll need to install the
JRE (this is installed on most machines
already). You can find a copy at
Sun.
Help
General parameters
- Inflow percentage
- As the clast ploughs, it gouges through the till. This option
allows you to set some percentage of the material gouged out of the
way to flow back into the gouge.
- Clast Width
- This is the clast length in the direction of ploughing and
also the length transfer to this.
- Clast Height
- The vertical length of the clast.
- Slope the clast ploughes into
- This is the slope angle in degrees. It could be
used to indicate prow buildup, but the physics of
this is less certain than that of ploughing into a slope.
- Initial debris fraction
- This is the amount, in kg, of sediment released from the ice
by the melting of 1kg of water. Note that this is not quite the
same thing as the ratio of sediment to water in the ice.
- Till internal friction
- The angle of internal friction of the till. 22 degrees is
appropriate for a silt-clay mix with some sand.
Buttons
- Switch Modes
- This button allows you to switch between the
two modes described above.
- Calculate for one speed/strength / Calculate for all speeds/strengths
- Runs the program. As a minimum the program will tell you it's
started and finished.
- Clear screen
- Clears the screen of results and messages.
- Set output to file
- This only appears if the program is run as an application. It
allows you to divert results to a text file, rather than the screen.
A few messages from the system are still shown on the screen.
Parameters for testing a single plough event
- Till residual strength
- The residual strength or residual supported stress of
the till. This is the amount of stress the till can support
after it has yielded. It is assumed in this model that
the yield strength is zero.
- Initial ice velocity
- The ice velocity in metres per year.
Parameters for testing a multiple ice velocities / till strengths
- Starting velocity / Ending velocity / Step between velocities
- Allows you to set up the first and last velocities to try. The
program will step between the two at a rate determined by the step
value. Each velocity will be tried to see if it produces the
requested ploughing length.
- Starting till strength / Ending till strength / Step between strengths
- Allows you to set up the first and last till strengths to try. The
program will step between the two at a rate determined by the step
value. Each till strength will be tried to see if it produces the
requested ploughing length.
- Minimum ploughed length / Maximum ploughed length
- Allows you to set a length the clast can plough. The
lengths between and including these two figures will
be looked for as the program tries various ice velocities and
till strengths. Any combinations that produce a length between
these two will be saved.
Changes from Evans, 1998
- The distribution of the meltout sediment has changed.
- The velocity difference between the clast and the ice are
now used as the lodgement criteria, not the drag force.
For details of the changes, contact Andy Evans.
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