HIGH WATER INTERVAL 



heavy ice — Any mass of sea ice more than 10 feet 

 thick. (59)' Obsolete. 



heavy minerals — Accessory detrital minerals of 

 high specific gravity, 2.8 or more, in rock or 

 sediments. Examples are magnetite, ilmenite. 



heavy sea — A sea in which the waves run high. 

 (73) 



heavy water — 1. Water in which the hydrogen of 

 the water molecule consists entirely of the heavy 

 hydrogen isotope of mass 2 (deuterium) . 



2. Written D.,0. Density, 1.1076 at 20°C. 

 It is used as a moderator in certain types of 

 nuclear reactors. 



3. The term is sometimes applied to water 

 whose deuterium content is greater than natural 

 water. 



(41) 

 heeling — Causing a ship to roll by mechanical 



means so as to enable it to gain headway when 



working in ice. (65) 



height — See wave height. 



height of the tide — The vertical distance from 

 chart datum to the surface water level at any 

 stage of the tide usually measured in f eet ; a pre- 

 determined reference plane. 



height-period combination — Waves with speci- 

 fied height and period. 

 height ratio — See ratio of ranges. 



hekistoplankton — See mu flagellates. 



hemipelagic-abyssal sediments — Deep sea de- 

 posits which contain terrestrial material. (2) 



herd — A congregation of gregarious wild animals 

 or of marine mammals. The term is most often 

 applied to pinnipeds (herds of seal coming 

 ashore to bear young) , but is also used in refer- 

 ence to cetaceans (the dolphin herd playing 

 through the swell ) . 



hermatobiolith — See hermatolith. 



hermatolith — Reef rock, also called hermatobio- 

 lith to indicate organic origin. (2) 



hermatrypic — Reef building. (2) 



herringbone cross-lamination — Thin layers of 

 sand cross-laminated in opposite directions in 

 alternating layers by frequently shifting cur- 

 rents in shallow water. 



hertz — (abbreviated Hz). A unit of wave fre- 

 quency, equal to one cycle per second. 



hervidero — See mud volcano. 



heteropod — One of a division (Heteropoda) of 

 pelagic, free-swimming gastropods in which the 

 foot is modified into a swimming organ con- 

 sisting of a flattened fin and a posterior tail. 

 The shell and body are transparent. 



heterotrophic nutrition — ^That process by which 

 an organism utilizes only preformed organic 

 compounds for its nutrition. See holozoic 

 nutrition, saprophytic nutrition, parasitic 

 nutrition, autotrophic nutrition, mixotrophic 

 nutrition. 



high — 1. In meteorology, elliptical for "area of 

 high pressure" referring to a maximum of 



atmospheric pressure in two dimensions (closed 

 isobars) in the synoptic surface chart, or a maxi- 

 mum of height (closed contours) in the con- 

 stant-pressure chart. 



Since a high is, on the synoptic chart, always 

 associated with anticyclonic circulation, the 

 term is used interchangeably with anticyclone. 

 (5) 



2. No longer commonly used in combination 

 form and not recommended by the ACUF for 

 the least depth of a general use type of feature 

 of any size, shape, or height. 



high energy environment — A region character- 

 ized by considerable wave and current action 

 which prevents the settling and accumulation 

 of fine-grained sediment smaller than sand size. 

 (2) 



higher high water — (abbreviated HHW). The 

 higher of two high waters occurring during a 

 tidal day where the tide exhibits mixed charac- 

 teristics. See mixed tide. 



higher high water interval — (abbreviated 

 HHWI). The interval of time between the 

 transit (upper or lower) of the moon over the 

 local or Greenwich meridian and the next higher 

 high water. This expression is used when there 

 is considerable diurnal inequality. See luni- 

 tidal interval. (68) 



higher low water — (abbreviated HLW). The 

 higher of two low waters of a tidal day where 

 the tide exhibits mixed characteristics. See 

 mixed tide. 



higher low water interval — (abbreviated 

 HLWI). The inter^'al of time between the 

 transit (upper or lower) of the moon over the 

 local or Greenwich meridian and the next higher 

 low water. This expression is used when there 

 is considerable diurnal inequality. See luni- 

 tidal interval. (68) 



highly stratified estuary — An estuary in which 

 salinity increases significantly from head to 

 mouth and surface to bottom ; characterized by a 

 density discontinuity separating surface river 

 flow and bottom sea water. 



high seas — See oceanic. 



high-speed layer — A layer in which the compres- 

 sional wave velocity is greater than in at least 

 one ad j acent layer. ( 2 ) 



high tide — See high water, 



high water — (abbreviated ITW; also called high 

 tide) . The highest lunit of the surface water 

 level reached by the rising tide. High water is 

 caused by the astronomic tide-producing forces 

 and /or the effects of meteorological conditions. 



high water full and change — (abbreviated 

 HWF&C) . See establishment of the port. 



high water inequality — See diurnal inequality, 



high water interval — (abbreviated HTWI). See 

 lunitidal interval. 



77 



