Plate riding: how
is the plate you are on moving now?: teacher's notes
Level
This activity is designed for
students aged 14 –16. It will consolidate work they have done on the rock
record and, more particularly, on plate tectonics.
Topic
This material can act as review
material to test students’ understanding of plate tectonics and the rock cycle. It highlights the links between
geological processes and plate tectonic processes.
Teaching points
This would be a useful exercise
to be set for homework or in the case of teacher absence. Teachers may prefer
students have access to their notes or text books to answer some of the more
demanding questions.
Timing
About 20 to 30 minutes to
complete the questions plus discussion to follow.
Answers to
questions
Q 1.
(a) It is moving towards the east.
(b) 3 cm per year (about as fast as your fingernails grow)
Q 2.
Everything on the plate is also moving at the same speed. Also it is so slow
that it would be impossible to detect.
Q 3.
Accept any answer for plate tectonics
that students may have met (identical rocks or fossils on continents that are
now split / ‘jigsaw fitting’ pattern of continents that were once joined /
evidence from magnetic stripes on ocean floors).
Q 4.
Global Positioning Systems (GPSs) can make very accurate measurements of the
Earth’s surface at intervals. They will fix a given point by latitude and
longitude on the surface and the movement of a point with respect to this can
then be measured.
Q 5.
No. While some move away from one another, others move towards one another
and some slide past one another.
Q 6.
(a) The plates concerned must be moving away from one another. The Eurasian
plate is moving away from the N. American plate, for example.
Since there is no hole in the ocean bed appearing, any gaps must be filled by
new plate material through igneous
activity at the mid-Atlantic ridge.
The pulling apart (tension) causes tensional faulting and sections of crust
can slide down forming a rift valley.
Not much sediment has accumulated since the oceanic plate is so new.
Apart from a bit of baking of one igneous rock by a newer hot one, there is
no metamorphic activity (there are no compressional pressures to cause wide
scale (regional) metamorphism).
.
(b) The plates concerned must be moving towards one another. There must be a collision zone ahead. This is the Eurasian
plate colliding with the Pacific plate (forming Japan).
Collision causes earthquakes in Japan - compressional faulting.
Due to the collision, one plate sinks (subducts
)
beneath the other – this plate partially melts and causes volcanic activity
(of a dangerous, explosive kind).
Over time the volcanic mountains are weathered and eroded producing sediment, the sediment
forms sedimentary rocks.
Plate pressure deforms the rocks into intense folds.
Heat and pressure due to the collision cause metamorphism of the rocks.
Q 7. Most igneous activity is at the margin behind
and at the margin in front (there is no igneous activity in the middle of
this plate). The activity behind is caused by magma rising at the mid-Atlantic ridge.
Activity ahead is caused by frictional forces as one plate subducts
below the other producing explosive volcanic activity.
Q 8. In the collision zone. Where there are
mountains being formed, these are readily attacked by weathering and erosion
processes. This causes high rates of sedimentary activity.
Q 9. In the collision zone. Heat and pressure due
to the collision causes metamorphism of the rocks.
Q 10. In the collision zone there can be intense
folding, and faulting and dangerous earthquake activity. It is much quieter
where plates are moving apart.
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