4 September 2008 MAR 110 MASTER Glossary 1MAR110 Natural Hazards and the Oceans MASTER Glossary 1. Abrupt Climate Change. Significant climate regime changes that occur very rapidly compared to the period of the change. For example the 3OF temperature decrease between the Medieval Warm Period to the Little Ice Age occurred in about 10years, while the LIA lasted about 500years before temperatures increased 3OF. 2. Active margin (between plates). A zone where ocean and continental plates collide. A deep trench is typically formed at the base of steep slopes. Shelves are narrow, and the shore is high and char-acteristically backed by a coast-parallel line of volcanoes. Earthquakes are common to great depths below the continental margin. 3. Albedo. The degree to which short wave solar radiation is reflected from any surface or object. 4. Basaltic. Referring to the most common liquid rock produced ·by a volcano, containing mainly magnesium, iron, calcium, aluminum, and some silicon. It forms a hard, but easily weathered, fine-grained, dark -grey rock. Volcanoes producing magma with these constituents are classified as basaltic. 5. Bathymetry. Ocean seafloor depths below sea level. 6. Benioff Zone. The zone at a depth of 700 km associated with earthquakes along a subduction zone. 7. Blizzard. Any wind event with velocities exceeding 60 km/hr, with temperatures below -6°C, and often with snow being blown within tens of meters of ground level 8. Bombs. Boulder-sized pieces of liquid lava blown out of an erupting volcano. 9. Bombs. (also see East-Coast Lows). 10. Caldera. The round depression formed at the summit of a volcano caused by the collapse of the underlying magma chamber that has been emptied by an eruption. 11. Continental Drift. The movement of continents relative to each other over 100s of million years; caused by convection in the interior earth. 12. Continental Shelf. That part of a continental plate submerged under the ocean, tapering off seaward at an average slope of less than 0.1 degrees, and terminating at a depth of 100-150 m in a steep drop to the ocean bottom. 13. Contour. A line on a chart, map, or section that connects equal values of a given dimension. A contour interval is the vertical distance between adjacent contour lines. 14. Conductivity. The ability of a fluid to conduct electrical currents. The conductivity increases with increased salt content. Salinity may be determined by measuring the conductance of seawater with an electronic device called a salinometer. 15. Convection. The upward transfer of heat through the movement of heated air or water parcels. 16. Convective Instability. A situation in which an air parcel, with a temperature greater than that of surrounding air (i.e. is less dense), rises upward - a process that is guaranteed when condensation leads to continued heating of the parcel. 17. Conveyor Belt. The thermohaline circulation mode of the ocean in which there is deep sinking of high-salinity, surface water in the polar zone that is cooled by releasing heat to the atmosphere and distant deep transport to the Indian and Pacific Oceans where it rises to the surface and is warmed. 18. Coriolis Deflection. The curvature of the trajectory of a freely moving water or air parcel to the right in the northern hemisphere (left in the southern hemisphere) as seen by an observer on a rotating Earth. 19. Coriolis Force. The apparent force caused by the Earth's rotation, through which a moving body on the Earth's surface deflects to the right in the northern hemisphere and to the left in the southern hemisphere. 20. Crust. The outermost shell of the Earth, 20-70 km thick under continents, but only 5 km thick under the oceans. It consists of lighter, silica-rich rocks, which flow on denser liquid rock making up the mantle. 21. Current. The motion of water as it flows down a slope and /or is pushed by wind stress or tidal forces. The velocity or speed of flow is usually expressed in centimeters per second, or for fast-moving cur-rents in meters per second or kilometers per hour. 22. Cyclogenesis. The process forming an extra-tropical, mid-latitude cell or depression of low air pressure. 23. Cyclonic circulation. Wind circulation around a low-pressure weather cell. In the Northern Hemisphere, when viewed from above, cyclonic winds follow a counter-clockwise rotation pattern.4 September 2008 MAR 110 MASTER Glossary 224. Datum. The reference level to which tide levels are compared. The datum planes commonly used are mean low water or mean lower low water, which are the average levels of low tides taken over a 19-year period. These are also the datum planes ("0" ft or "0" m) used in constructing bathymetric charts. 25. Deep-Ocean Floor. A zone characterized by abyssal plains of depositional (sedimentation) origin, abyssal hills, seamounts (volcanoes), guyots (or flat-topped seamounts), channels, and gaps and local rises. 26. Density. Defined as the mass per unit volume of a substance. In the metric system, the units for liquids are grams per cubic centimeter (gm/cm3). For purposes of comparison only, seawater density may be taken as 1.0250 gm/cm3; whereas fresh water is 1.000 gm/cm3. 27. Density Anomaly. The departure of seawater density from that of fresh water (1.000 gm/cm3) times 1000; which for an oceanic density of 1.025 gm/cm3 is 25. 28. Diurnal tides. Tides occurring once daily, with one high and one low tide per lunar day. 29. Downwelling. A downward movement (sinking) of surface water caused by onshore Ekman transport, converging currents, or when a water mass becomes more dense than the surrounding water. 30. Dynamic Topography. The irregularities in the sea surface produced by wind or differences in density, usually expressed in dynamic meters or fractions thereof. This topography changes with time and the seasons. 31. East-Coast Lows. Very intense storms that develop at mid-latitudes on the seaward, eastern sides of continents. Such lows develop over warm ocean water in the lee of mountains and are dominated by intense convection, storm waves, and heavy rainfall. Events where wind velocities reach in excess of 100 km hr-1 within a few hours are called 'bombs'. 32. Easterly Wave. In the tropics, pressure tends to increase parallel to the equator with easterly winds blowing in straight lines over large distances. However, such airflow tends to wobble, naturally or because of some outside forcing. As a result, isobars