American Samoa, Shaded Relief and Colored Height

The topography of Tutuila, largest of the islands of American Samoa, is well shown in this color-coded perspective view generated with digital elevation data from the Shuttle Radar Topography Mission (SRTM.)

The total area of Tutuila is about 141.8 square kilometers (54.8 square miles), slightly larger than San Francisco. The large bay near the center in this view is Pago Pago Harbor, actually a submerged volcanic crater whose south wall collapsed millions of years ago. Adjacent to the harbor is Pago Pago, the capital of American Samoa, and to the left (west) of the harbor in this view is Matafao Peak, Tutuila’s highest point at 653 meters (2,142 feet).

On September 29, 2009, a tsunami generated by a major undersea earthquake located about 200 kilometers (120 miles) southwest of Tutuila inundated the more heavily populated southern coast of the island with an ocean surge more than 3 meters (10 feet) deep, causing scores of casualties. Digital topographic data such as those produced by SRTM aid researchers and planners in predicting which coastal regions are at the most risk from such waves, as well as from the more common storm surges caused by tropical storms and even sea level rise.

Two visualization methods were combined to produce the image: shading and color coding of topographic height. The shaded image was derived by computing topographic slope in the northeast-southwest direction, so that northeast slopes appear bright and southwest slopes appear dark. Color coding is directly related to topographic height, with green at the lower elevations, rising through yellow and tan, to white at the highest elevations. The image was then projected using the elevation data to produce this perspective view, with the topography exaggerated by a factor of two.

http://photojournal.jpl.nasa.gov/catalog/PIA11965