1. In the Figure 1 schematic view of the ocean bottom, the vertical scale is given in kilometers (km). This vertical scale is vastly different from the horizontal scale. The vertical distance between scale markings is [(1)(10)(100)] km. 2. The ocean trench in the schematic view has a maximum depth of [(8)(80)(800)] km below sea level. 3. The distance between scale markings on the horizontal scale is 100 km. Comparison of the vertical and horizontal scales indicates that the vertical scale is exaggerated [(10)(100)(1000)] times relative to the horizontal scale. 4. The right portion of Figure 1 describes general characteristics of the ocean bottom in coastal areas that are tectonically passive (not near a plate boundary). The left portion of the figure generalizes tectonically active coastal areas. Tectonically active regions, typically associated with convergent plate boundaries, experience relatively frequent earthquakes and/or volcanic activity. You examined the locations of plate boundaries in Investigation 2A. Convergent plate boundaries are more closely associated with the [(west)(east)] coasts of the Americas.
5. The east coasts of North and South America, with their generally broad continental margins similar to the right profile in Figure 1, are tectonically [(active)(passive)]. 6. The west coasts of the Americas, with relatively narrow continental margins similar to the left profile in Figure 1, are tectonically [(active)(passive)]. Figure 2 displays a section of the South American west coast as an example, with a dark-blue ocean trench in close alignment to the green coastal land areas. 7. In the Figure 3 cross-section, water depth and land elevation are reported in m with the 0 m line representing sea level. Horizontal distance is measured in km from 75° W eastward to 70° W. The total length of the cross-section is about 500 km.
Compare this vertical cross-section with Figure 1. Figure 3 most closely resembles the [(left)(middle)(right)] portion of Figure 1. 8. The oceanic trench reaches a maximum depth of approximatedly 7400 m in the vertical cross-section. The maximum depth is at a distance of about 80 km from the shoreline. The nearly horizontal continental shelf extends westward from the shoreline about 10 km before the profile of the ocean bottom indicates a relatively steep decline that continues until the maximum depth is reached. According to Figure 1, this decline primarily composes the [(continental rise)(continental slope)(abyssal plain)].
9. Oceanward of the oceanic trench, the ocean bottom first rises and then levels off to a depth of approximately 3900 m, making the deepest part of the ocean trench about [(1400)(2400)(3500)] m below the bottom of the abyssal plain ocean bottom west of the trench. 10. This Figure 3 vertical cross-section exhibits a profile consistent with a tectonically [(passive)(active)] coastal region. 11. The horizontal distance in Figure 5 is measured in km from 77° W eastward to 71° W, covering a total length of about 550 km. The average maximum depth of the nearly horizontal eastern portion of the profile is about 4400 m. Compare this vertical cross-section with Figure 1. Figure 5 most closely resembles the [(left)(middle)(right)] portion of Figure 1. 12. In the Figure 5 profile, the coastline is within a few kilometers of the western end of the vertical cross section.
From the coastline, water depth increases very gradually to about 40 m at 140 km from shore (western end of the profile). This segment of the vertical cross-section resembles the continental [(rise)(slope)(shelf)] as labeled in Figure 1. 13. Beginning at 140 km from land, the ocean bottom profile “breaks”, that is, it begins dropping off significantly with an increase in distance from the shoreline. At about 180 km distance from land at a depth of near 2400 m, there is a distinct change to a less steep profile.
The segment of the profile from 140 km to 180 km from land is the [(rise)(slope)(shelf)] portion of the continental margin as displayed in Figure 1. 14. The segment of the ocean bottom profile immediately beyond 180 km distance from land is likely the [(rise)(slope)(shelf)] component of the continental margin as displayed in Figure 1.Beyond 400 km from land, the bottom exhibits flat, featureless abyssal plain characteristics. In this part of the North Atlantic Ocean, this occurs at a depth of about 4400 m. 15. This southeastern U.S. vertical ocean cross-section is consistent with a tectonically [(active)(passive)] continental margin as described earlier in this investigation.