Our tectonic
processes videos on YouTube
One of the first issues we had to consider for the
animations was the scale of the diagrams, as we wanted the animations to be realistic. It soon became clear that to really emphasise
the key concepts and processes we would have to use an exaggerated scale for
some areas. As most of the “action” we wanted to
illustrate occurs in the crust, we exaggerated the thickness of this layer. The
crust is the thinnest layer of the Earth. If you could shrink the Earth down to
the size of an apple the crust would be comparable to the skin (perhaps even
thinner). The oceanic crust reaches a maximum of around 8 km.The average
thickness of the continental crust is around 35 km, with a maximum thickness of
around 90 km. The lithosphere is the outer solid part of the Earth and includes
the crust and uppermost mantle (lith = rock). The lithosphere varies in
thickness, with an average thickness of around 100 km and extending up to
around 280 km in some areas. Therefore, to show our volcanoes forming and the
rifting process we needed to amplify the size.
The volcanoes in
this animation have been exaggerated in scale in relation to the thickness of
the crust and lithosphere, although Mauna Kea in Hawaii measures over 10 km
from base to peak.
A key concept we wanted to illustrate was how melting of the
asthenosphere at divergent plate boundaries occurs. The asthenosphere is
considered a rheid (a solid which deforms slowly over time). As the lithosphere starts to pull apart,
faults begin to form in the brittle crust. The lithosphere starts to thin,
which leads to a reduction in overlying pressure on the asthenosphere below it.
The reduced pressure allows the asthenosphere to partially melt and this is known
as decompression melting. The rifting movement of the crust enables the magma
to rise upwards and fill the spaces.
- This short video clip shows how a reduction in pressure can cause boiling
- Here is an activity relating to decompression melting
A misconception that we particularly wanted to address was
that of the melting at subduction zones. It is often taught that as a plate subducts it rapidly melts. This is
not the case. Plates subduct at a much faster rate than heat conduction and the
subducting plate stays cool until great depths. Subduction zones form when two tectonic plates converge and one, or
both, is oceanic lithosphere. The denser
(oceanic) plate sinks into the mantle. As it sinks deeper into the mantle, the
pressure increases. At around depths of 100 km, pressure is such that
metamorphism of the hydrous minerals contained in the oceanic plate, such as
amphiboles, occurs. This causes a release of volatiles (mainly water). The
water will rise upwards into the hot mantle rocks, lowering their melting
temperature. This enables some minerals
to melt and rise up towards the surface, in a process known as partial melting.
- Here is a delicious activity exploring partial melting
- Here is another hands-on activity that you can do to show partial melting
Although Earth Science studies ancient processes, it is a
relatively young science. There is still so much to be discovered and further research
is always advancing our understanding regarding these processes. We hope that
the animations can be used to help explain current scientific understanding of
these processes and look forward to creating future iterations, with development
of our knowledge.