World slope map

A colored slope map (scale 1:80,000,000) was generated from digital land and sea floor elevations at 5‐min spacings from data tapes from the National Geophysical Data Center. Slope analysis is facilitated by examining the average slope in 250‐m altitude‐depth intervals both globally and in each of eight tectonic plates. The most striking feature of the map is the multiple parallel bands of steep slope at subduction zones. Submarine volcanic chains produce zones of steep slope that show little degradation at the scale of the map since the Cretaceous. The average slope, or roughness, of spreading ridges decreases exponentially with increasing spreading rate. The passive continental margins generate a steep zone at 1–2 km depth. The lowest average global slope (0.2°) occurs at sea level and reflects the base level that the sea provides for subaerial erosion and the upper limit for marine sedimentation. Slope minima also are caused by the abyssal plains at 4–6 km depth and by glacial ice caps at 3 km elevation.