Subduction

You can't always just make new plate.

The model is that when oceanic plate runs into the lighter continental plate, it gets pushed underneath.

The subducted plate melts as it sinks, and lighter parts try to float to the top.

Result: volcanos

In addition, the oceanic crust is not likely to just smoothly slide under the continent.

• The two rock plates should stick for a long time.
• Then as the force builds, they should slip suddenly.
• Result: earthquake.
• If the earthquake is under or near the ocean, it generates a tsunami.
• The longer the plates stay stuck, the more the force builds up, and the stronger the earthquake is.
• There has not been a major earthquake in the Pacific Northwest at least since 1850 or so.
• There is evidence that major earthquakes occur near the Oregon coase every couple of hundred years.
• But there also evidence that the most recent such earthquake occured couple of hundred years ago.

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On one hand, all this evidence in the Pacific Northwest lends support to the theory of plate tectonics. It is also a matter of concern for public safety.

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