Lab 7 Objectives: Igneous Rocks, and Topographic and Geologic Maps Learn to recognize the igneous rock textures Identify felsic, intermediate, and mafic compositions Be able to identify igneous rocks using the igneous rock chart Become familiar with the distribution of igneous rocks in the United States and California. To become familiar with topographic maps. I. TOPOGRAPHIC MAPS and the eruption of Mt. St. Helen's 1. Indicate which is the 'Before' map and which is the 'After' map. 2. What is the contour interval for these maps? elevation and Shape of A. On the 'Before' map 1. Why are the contour lines wiggly? these contour lines are wiggly because the indicate elevation and Shapes of the land. 2. If you dropped your camera at the second 0 in '2500', describe the compass direction that it would roll. Use either azimuth or quadrant, whichever you feel most comfortable with. (Note that north is to the right!!) 3. On the 'Before' map complete the profile by transferring the elevations to the cross-section below the map. 4. Constrain the elevation of the highest point on the volcano: B. On the 'After' map 1. Which side of the mountain was most affected by the eruption? (Remember, north is to the right) 2. On the 'After' map complete the profile by transferring the elevations to the cross-section below the map. 3. In the bottom of the new crater, why are the contour lines so widely spaced? (i.e., what do widely spaced contour lines indicate?) 4. Describe the relationship between contour line spacing and slope. 5. Constrain the elevation of the highest point on the mountain: 5. How has the elevation of the mountain changed as a result of the eruption?
