Answer to Question 1At convergent boundaries the compressional forces that occur as a result of two plates
pushing together produces violent geological activity. One plate is subducted underneath the
other plate, the leading edge pulled downward by gravity into the mantle. Lithospheric crust
will melt as the plate plunges downward and its temperature rises. Volatile components, such
as water and carbon dioxide, are driven off and rise toward the overriding plate. Magma rises
to the surface and causes volcanic eruptions and earthquakes. Earthquakes that form in these
regions may occur at greater depth along the sliding edge of the subducting plate as it
descends into the mantle.
Answer to Question 2In 1965, the ideas of continental drift and seafloor spreading were integrated into the
overriding concept of plate tectonics, primarily by the work of John Tuzo Wilson, a
geophysicist at the University of Toronto. In this theory Earths outer layer consists of about
a dozen separate major lithospheric plates floating on the asthenosphere. When heated from
below, the deformable asthenosphere expands, becomes less dense, and rises. It turns aside
when it reaches the lithosphere, lifting and cracking the crust to form the plate edges. The
newly forming pair of plates (one on each side of the spreading center) slide down the
swelling ridgesthey diverge from the spreading center. New seabed forms in the area of
divergence. The large plates include both continental and oceanic crust. The major plates
jostle about like huge slabs of ice on a warming lake. Plate movement is slow in human
terms, averaging about 5 centimeters (2 inches) a year. The plates interact at converging,
diverging, or sideways-moving boundaries, sometimes forcing one another below the surface
or wrinkling into mountains.
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