The Earth Contents

2. Plate Tectonics

Destructive plate motion occurs where plates are converging

At subduction zones, plates are converging and continued movement is only possible if one plate can be destroyed. The denser plate is forced beneath the lighter plate and the descending plate is melted as it enters the upper mantle, with some of the molten material being returned by volcanic activity. The location where the plate leaves the surface and is driven down into the mantle is always marked by a deep trench (up to 10 km depth). This trench marks the line along which the two colliding plates make contact. As the weaker plate descends the marine sediments are scraped off by the over-riding plate and are plastered on to the trench wall. These shavings, and the buckling of the colliding plates, form mountain ranges.

What type of plate motion would you associate with trenches?