How Are Volcanoes Related to Plate Tectonics?
ES0901  Northwestern United States 3-D View

In this region, the north-south trending ridges on the seafloor represent a divergent boundary. Volcanism along this ridge is quiet and relatively frequent. An increase in water temperature, detected by underwater instruments, or a series of small earthquakes is often the only evidence that an eruption has occurred along this mid-ocean ridge.

The line connecting sections of the divergent boundary is a transform boundary. Visualize the plate on the north side of this line moving east compared to the plate on the south side of the boundary.

The deep trench parallel to the coastline is a subduction zone, where the plate on the left dives below the one on the right. Magma is generated east of the subduction zone, where subducted material reaches a depth at which it melts. Eruptions of subduction-related volcanoes are not very frequent, but when they do occur, they are very explosive.

  !   Follow the instructions on the left to examine these features in three dimensions.

 

 
   

4. Sketch the cross section of this region onto your worksheet.

5. Where does the magma for volcanism at the rift zone come from?

6. What material is melted to provide magma to the Cascade volcanoes?

 
   

 Step:   1   2   3   4