Compute the gradient of the outer base of the Okmok Caldera along line EF. Use the coastline closest to Point E as the starting point for measuring horizontal distance, and the northwest rim of the caldera as the stopping point. It may be easiest to use the graphic map scale to measure out a distance of four or five miles, and then determine the elevation change over that distance.

Question

The following questions are based on Map T-2, the “Umnak, Alaska,” topographic map (scale 1:250,000; contour interval 200 feet). In this problem, you will estimate the height of the original Okmok volcano before the caldera was formed. (You may also determine the elevation changes and distances needed to make these calculations by using Google Earth™.)

Gradients can be used to estimate an elevation increase over a given distance. (See Exercise 34 for a review of gradients.) For example, if a mountain has a gradient of 1000 feet per mile, we can estimate that over a horizontal distance of five miles, the elevation will increase by 5000 feet.



5 miles * 1000 ft>mi = 5000 foot elevation increase over five miles

Answer 1