(1) [sea ice] a smooth hill of ice that forms on the sea ice surface from eroding ridges, particularly during the summer melt; the formation of hummocks is similar to young mountain peaks with steep slopes that erode into smooth, rolling hills. (2) [frozen ground] Small lumps of soil pushed up by frost action, often found in uniformly spaced in large groups. Hummocks can form in areas of permafrost or seasonally frozen ground, and are one of the most common surface features of the Arctic.
Hummocks make the sea ice surface appear as rolling hills. (Photo courtesy of Ted Maksym, United States Naval Academy.)
a form of weathering that affects all rocks; water freezes in pores and cracks, which leads to an increase in specific volume (vol/unit mass) of the water, producing stress that is greater than the tensile strength of all common rocks; ultimately leads to shattering and fracturing of the rocks.
an instrument which measures the water vapor content in the atmosphere; there are several different means of transduction used in measuring this quantity and hence various types of hygrometers; these are: a) the psychrometer, which utilizes the thermodynamic method; b) the class of instruments which depends upon a change of physical dimension due to absorption of moisture (hair hygrometer, for example); c) those which depend upon condensation of moisture (dew point hygrometer); d) the class of instruments which depend upon the change of chemical or electrical properties due to absorption of moisture, and some others.
a core sample drilled from the accumulation of snow and ice over many years that have recrystallized and have trapped air bubbles from previous time periods, the composition of which can be used to reconstruct past climates and climate change; typically removed from an ice sheet (Antarctica and Greenland) or from high mountain glaciers elsewhere.
the boundary at any given time between open water and sea, river or lake ice of any kind, whether drifting or fast; may be termed compacted when it is clear-cut, or open when it forms the indefinite edge of an area of dispersed ice.
Aerial view of the sea ice edge. (Photo courtesy of Todd Arbetter, National Snow and Ice Data Center.)
a suspension of numerous minute ice crystals in the air, reducing visibility at the earth's surface; the crystals often glitter in the sunshine; ice fog produces optical phenomena such as luminous pillars and small haloes.
a form of tabular berg found in the Arctic Ocean, with a thickness of 30 - 50 meters (33 to 55 yards) and an area from a few thousand square meters to 500 square kilometers (123,550 acres); ice islands often have an undulating surface, which gives them a ribbed appearance from the air.
from the point of view of the submariner, a downward-projecting ridge on the underside of the ice canopy; the counterpart of a ridge; ice keels may extend as much as 50 meters (55 yards) below sea level.