Stratovolcanoes – Mt. Saint Helens, WA. Fly to Mt. Saint Helens in the Cascade Range of western Washington, and then turn on the Mt. Saint Helens Contour Map overlay. The brown lines are contours (lines of equal elevations). Use the Ruler tool to determine the horizontal distance (ft) between the Problem 7 placemarks and then subtract the elevations (ft) for each placemark from the contour map to determine the relief (vertical distance). Find the slope angle of Mt. Saint Helens using the following formula (this value is representative for many composite cone volcanoes): slope angle = tan–1 (relief ÷ horizontal distance) Choose one: 5°–10° 15°–20° 25°–35° 35°–45°