rise— a broad elevation that rises gently and generally smoothly from the sea floor. 

 saddle— a low part, resembling in shape a saddle, in a ridge or between contiguous seamounts. 

 seachannel—a continuously sloping, elongated depression commonly found in fans or plains and custo- 

 marily bordered by levees on one or two sides. 

 seamount— an elevation rising generally more than 1,000 meters and of limited extent across the summit. 

 shelf— a zone adjacent to a continent (or around an island) that extends from the low water line to a 



depth at which there is usually a marked increase of slope towards oceanic depths. 

 shelf valley— a valley on the shelf, generally the shoreward extension of a canyon, 

 shoal— a hazard to surface navigation composed of unconsolidated material. 

 siZZ— the low part of a gap or saddle separating basins, 

 slope— the slope seaward from the shelf edge to the beginning of a continental rise or the point where 



there is a general reduction in slope. 

 spur— a subordinate elevation, ridge, or rise projecting outward from a larger feature. 

 tablemount (or guyot)—a seamount having a comparatively smooth, flat top. 

 terrace— a relatively flat horizontal or gently inclined surface, sometimes long and narrow, which is bounded 



by a steeper ascending slope on one side and by a steeper descending slope on the opposite side. 

 tongue— an elongate (tongue-like) extension of flat sea floor into an adjacent higher feature. 

 trench— a long, narrow, characteristically very deep and asymmetrical depression of the sea floor, with 



relatively steep sides. 

 trough— a long depression of the sea floor characteristically flat bottomed and steep sided, and normally 



shallower than a trench, 

 valley— a relatively shallow, wide depression, the bottom of which usually has a continuous gradient. (This 



term is generally not used for features that have carayon-like characteristics for a significant portion 



of their extent.) 



Italicized terms in the above definitions are themselves defined in the list. Asterisks indicate minor- 

 feature terms approved by BGN. With few exceptions, including minor-feature terms and definitions, the 

 terminology agrees with that used by the IHO. 



The terms arch, arrugado and deep have not been incorporated in the above list, but do appear in 

 the names Hawaiian Arch, Guadalupe Arrugado, Challenger Deep, Emden Deep, and Horizon Deep which 

 have been approved by the BGN on the basis of the names' established usage. Hawaiian Arch is a low bulge 

 around the southeastern end of the island of Hawaii, Guadalupe Arrugado is an area of subdued corrugations 

 off Baja California, Challenger Deep, Emden Deep, and Horizon Deep are deep holes in the Mariana Trench, 

 Tonga Trench, and Philippine Trench, respectively. The terms should not be applied to new features. 



NAME PROPOSAL FORM 



Undersea name proposal forms are provided in this publication to facilitate submittal and expedite 

 approval and promulgation of names. Anyone may propose a name for an unnamed undersea feature that 

 has been adequately identified as to tj^ie and geographic location. 



Users are encouraged to submit a separate form for each name proposed, copying the form if necessary, 

 and filling in all the blanks that are pertinent. They should give appropriate coordinates of latitude and 

 longitude and read closely enough to sufficiently identify the feature. 



For "feature type," use the appropriate term from the list of "TERMS AND DEFINITIONS" in this 

 gazetteer. This term should be used also as the generic in the name. If the feature is of a kind not covered 

 by these terms or definitions, explain in a supplementary note. 



IX 



