HYPSOMETRY 



metric height is given by the hydrostatic 

 equation. (5) 



hydrostatic instability — See instability. 



hydrostatic pressure — The pressure at a given 

 depth due to the weight of the water column 

 above that depth. 



hydrotroilite — A black, finely divided colloidal 

 material {FeS) reported in many muds and 

 clays. 



hydrozoan — (or hydroTnedusa) . One of a class 

 (Hydrozoa or Hydromedusae) of coelenter- 

 ates. The highly branched polyp or hydroid 

 stage of many members is an important compo- 

 nent of fouling. 



hyperpycnal (more dense) inflow — Sediment- 

 laden water flowing down the side of a basin and 

 then along the bottom as a turbidity current, 

 with vertical mixing inhibited because the dense 

 water seeks to remain at the lowest possible level. 

 Delta formation by such flow is most frequent at 

 the mouth of submarine canyons. (2) 



hypolimnion — The layer of water below the 

 thermocline in a fresh water lake or pool; 



distinguished from epilimnion, the layer above 



the thermocline. 



hypopycnal (less dense) inflow — Sediment-laden 

 fresh water discharging into denser saline water 

 of the ocean. The fresh water spreads over the 

 surface of the sea water forming a lunate bar if 

 discharge is small or cuspate, arcuate, or bird- 

 foot deltas if discharge is large. (2) 



hypothermia — A fall in the temperature of an 

 animal body below the usual level. This state 

 is brought about when the homeostatic mecha- 

 nisms fail to maintain adequate production of 

 heat under conditions of extreme cold. (5) 



hypsographic chart — A chart or part of a chart 

 showing land or submarine bottom relief in 

 terms of height above datum ; also a hypsomet- 

 ric chart which is a chart showing gradients by 

 means of tints. Hypsography or hypsometry 

 is the science of measuring or describing eleva- 

 tions above a datum. 



hypsography — See hypsographic chart. 



hypsometric chart — See hypsographic chart. 



hypsometry — See hypsographic chart. 



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