Click here for Activity 7.

The students must answer the following questions:

**Calculate the tilt angle between the 0-30 and 60-90 mm contours. Hint: a=30-0=30 mm and 90-60=30 mm, b=distance between contours=3.6 km and 1.4 km, respectively.**

To calculate the tilt angle, the numbers must be in the same units. To convert km to mm:3.6 km x 1000 m x 1000 mm = 3,600,000 mm. ------ ------- 1 km 1 m

Repeat for 1.4 km. Plugging the numbers into the equation yields:tan A = 30 mm and A = 1.5 x 10-7 degrees and ------------ 3,600,000 mm tan A = 30 mm and A = 3.7 x 10-7 degrees. ------------ 1,400,000 mm

Notice that the tilt between the 60-90 mm contours is more than twice the tilt between the 0-30 mm contours.**Estimate the tilt angle near the center of the uplift. Assume maximum uplift is 115 mm at the center of the 105 mm contour.**

a=115-105=10 mm. b is determined using the map scale and is equal to 1.5 km (1,500,000 mm). Plugging the numbers into the equation yields: tan A = 10 mm and A = 1.1 x 10-7 degrees. ------------ 1,500,000 mm**Do you think a geologist standing on the summit of the volcano would detect the change in tilt?**

No. The angles are too small and require very sensitive instruments to measure.**Which location has the greatest tilt angle?**

The location on the flank of the volcano has the greatest tilt angle.**Is the maximum tilt the same, two times greater, five times greater, or ten times greater than the tilt at the other two locations? (circle one)**

The maximum tilt is about two times greater than the other measurements.**To maximize the utility of a tiltmeter, should it be placed at the center, flank, or edge of an area of uplift? (circle one)**

Since the greatest changes occur on the flanks of the uplift, this is the best location for a tiltmeter. The small changes in tilt at the top and edges of the uplift would be harder to detect.

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