Lab Exercise 3

Physical Geology Helpful Lab Hints

Exercise 3: Igneous Rocks

a. Examine the satellite images on page 123 carefully.
- Mt. St. Helens is in the southwest corner of Washington state.
- Note the ring-shaped cloud in the 9:15 photo. Draw a circle representing the outline of the cloud on the map on page 124.
- On the remaining photos, note that the cloud gets progressively larger, although not in all directions. Use your best judgment to determine the extent of the cloud and draw the boundary for each time on the map on page 124. (Be sure to label each boundary with the time.)
b. & c. Complete the table on page 122.
- Write the time of each image in the first column.
- Measure the maximum distance of the far edge of the ash cloud from Mt. St. Helens in the second column. Use the map on page 124, there is a scale in the lower left hand corner. For the 16:15 boundary, be sure to measure in both miles and kilometers.
- The third column (travel time) is the time between when the eruption occurred (appx. 8:30) and the time the image was taken. For example: for the image taken at 9:15, the travel time is 45 minutes OR .75 hours, and for the image taken at 10:15, the travel time is 1 hour, 45 minutes OR 105 minutes OR 1.75 hours.

f. Calculate the overall velocity between the eruption and the final photo.

example:

time	distance	travel time
16:15	100 km OR 60 mi	7 hr.,45 min. OR 7.75 hr OR 465 min.

You may calculate each of the three velocities by using the appropriate units from the table.

You may calculate one velocity and convert to the other units using the factors provided.