Plateaus
Alava plateauis caused by a large amount of less viscous lava that flows over a large area.
When it solidifies, it creates a large, flat surface of igneous rock. Some plateaus are huge, like
the Columbia Plateau in Washington, Oregon, and Idaho that covers over 161,000 square
kilometers (63,000 square miles).
Land Area
Another important land formation created by lava is islands. The Hawaiian Islands are
formed from solidified lava from shield volcanoes that have grown over the last 5 million
years (Figure 8.29). The land area grows as lava continues to solidify on the coast or
emerges from beneath the water.
Figure 8.29: Solidified lava flows created the island of Hawaii. ( 18 )Landforms from Magma
Of course, not all magma reaches the surface. Sometimes magma stays beneath the ground
where it solidifies. These formations are calledintrusions(Figure8.30). Because they
form underground, they only become land formations if they arrive at the surface of the
Earth. This occurs because of weathering, erosion and plate tectonics. In other words, when
tectonic plates collide, they create mountain ranges where one plate is lifted in a subduction
zone. This lifting (which occurs at a rate of centimeters per year) and subsequent erosion
can eventually uncover intrusive rock formations. As erosion removes the topmost rocks and
soil, solidified magma is exposed in the same form in which it cooled and solidified many
years before.