Use the Ruler tool to determine the direct distance from the trench to the volcanic peaks immediately to the east. Make several measurements, and record the approximate latitude of your measurement and the trench-volcano distance in the spaces provided below. Distance Latitude of Observation Trench-Volcano Distance 259 km 45 degrees N 318 km 43 degrees N 370 km 45 degrees N 638 km 40 degrees N Research has shown that melting begins to occur as the subducted plate arrives at a depth somewhere between 100 and 120 km below Earth's surface. If the less dense molten rock rises to the surface, it may erupt as a volcano. 14. Refer to the diagram and formula described in placemark A or B, and the average trench-to- volcano distance you recorded above, to determine the descent angle of the Juan de Fuca plate beneath the North American continent. Descent angle of the Juan de Fuca plate = About 20 degrees descent angle