128 NAUTICAL CHAKT MANUAL 



TahUmownt A seamount rising more than 500 fathoms from the sea floor 



and having a comparatively smooth, flat top with minor 



irregularities. 

 Terminal moraine A moraine formed across the course of a glacier at its farthest 



advance, at or near a relatively stationary edge, or at places 



marking the termination of important glacial advances. 

 Terrace A bench-like feature bordering an elevation of the sea floor. 



A terrace does not include the continental shelf or island 



shelf but may include bench-like features on the shelf. 

 Tidal marsh or flat Any marsh or flatland, the surf ace of which is wetted by a tidal 



flow. 

 Tide gate An opening through which water may flow freely when the 



tide sets in one direction, but which closes automatically 



and prevents the water from flowing in the other direction. 

 Tide rips (0-18) Turbulence caused by the meeting of conflicting tidal currents 



or by a tidal current flowing over irregular bottom. 

 Tongue A long, narrow strip of land, projecting into a body of water; 



a long, narrow body of water indenting the land or bounded 



by islands. 

 Topography The configuration (relief) of the land surface; the graphic 



delineation or portrayal of that configuration in map form, 



as by contour lines. 

 Trench A long, narrow, depression of the sea floor, having relatively 



steep sides. 



Tributary Any stream which feeds a larger stream or lake. 



Trough A long depression of the sea floor, having relatively gentle 



sides, normally wider and shallower than a trench. 

 Tundra One of the level or undulating treeless plains characteristic of 



arctic regions, having a black muck soil with a permanently 



frozen subsoil. 

 Upland A highland; groimd elevated above the lowlands along riverp 



or between hills. 

 Valley A relatively shallow, wide depression with gentle slopes, the 



bottom of which grades continuously downward. This term 



is used for featiu-es that do not have canyon proportions in 



any significant part of their extent. 

 Volcano An opening in the earth's crust through which lava and ash 



issue; a mountain (usually conical) formed wholly or in 



part by such volcanic action. 



Wash A broad, dry bed of a stream. 



Watershed The area drained by a stream. 



Wharj (G-18) A structure extending parallel to the shoreline so that vessels 



may lie close alongside to receive and discharge cargo. 



