Student's Abstact:
The Earth's surface consists of many different moving
plates creating plate tectonics. The Pacific plate in specific has all different
plate boundaries around its edges. Looking at the Pacific plate as the plate
that is moving one can determine the relative velocity and direction of the
plate by using Euler Poles. The Pacific plate moves in the same general direction
throughout the plate boundaries. Yet its velocities vary with the boundaries.
At spreading boundaries such as the spreading ridge of the Eastern Pacific
Rise which is a boundary between the Pacific plate and the Nazca Plate a
total velocity of 14.3 cm/yr was observed. On the other side of the Pacific
plate at subduction zones such as the New Guinea Trench, velocities of similar
magnitude can be observed. This tells us that in part, the Pacific plate
gets destroyed as fast as it is created. Relative to the creation and
destruction velocities, velocities along transform faults such as the San
Andreas Fault are smaller. The movements along the transform faults
have a smaller velocity because of the direction the plate is moving. The
creation and destruction of the plate creates a pull and push effect which
is why the plates move a lot faster along these boundaries. When a plate
moves along another plate in a transform fault, the velocity is defined by
the overall speed of the plates moving past each other. There is a lot of
friction in this area and the velocity is therefore smaller than that of
the ridge/trench system. The plate overall is moving in a West, North West
direction.
TA comments:
This is a great abstract, although the interpretations for the transform
faults are a bit off, but the student is still doing what we want to see:
thinking about your results in terms of geology and inferring underlying
processes/reasons for observations. Making connections between things
like fast spreading rates on one side of the Pacific with fast subduction
on the other is exactly what we were hoping you would see.
Student abstract:
In this lab we are learning how to calculate the velocity of a point on one
plate relative to another plate. Specifically, we are using circum-Pacific
points in order to ascertain the velocity of the Pacific Plate relative to
the surrounding plates. As these motions occur on a globe, we will be using
spherical geometry in conjunction with both the appropriate Euler poles and
angular velocity vectors to determine the magnitude of the relative motion
at each location point. The results of these motions reveal a concentration
of spreading centers and transform margins on the Eastern edge of the Pacific
Plate, while convergent margins are found on the Western edge. There is also
an interesting occurrence of highly oblique convergence in the South Pacific
in the region containing New Zealand's South Island and the Macquarie Ridge.
The locations of these boundaries combined with the high rates at which the
Pacific Plate is moving westward support the idea that the Pacific Ocean
is closing, and quite quickly at that.
TA comment: This is a good abstract. A definition of Euler poles squeezed
into the first or second sentence would have been nice. The last sentence
was what got this student a high grade for the abstract even though it was
a bit short.
Both abstracts:
Neither abstract spends time describing in detail the procedure. Generally
you don't want to talk too much about procedure and you should try to focus
more on the big picture of the lab and why you did it.
A sentence describing the general northwesterly motion of the pacific relative
to the surrounding plates would have convinced us that the student fully
understands what we are trying to teach them, or in other words a grade of
50 out of 50.
Happy abstracting,
Alex