K-Ar Dating - See potassium-argon dating.

K-Selected Species (Logistic Strategy) - A long-lived species that produces only a few, often fairly large progeny. Compare with r-selected species. Also see r- and K-Selection.

Kame - A steep conical hill composed of glaciofluvial sediments. This feature forms when glacial crevasses and depressions in stagnant glacial ice are filled with sand and gravel deposits derived from sediment in meltwater.

Kame Terrace - A long flat ridge composed of glaciofluvial sediment. This feature forms along the margin of a valley glacier, where the glacial ice meets the valley's slope. The sediment that makes up these features is deposited by laterally flowing meltwater streams.

Kaolin - A type of clay mainly composed of the mineral kaolinite. For hundreds of years, kaolin has been used by humans to manufacture pottery, bricks, cement, plaster, and insulating materials.

Kaolinite - A type of clay mineral that is widespread in tropical and subtropical regions of the world. Chemically, it can be described as a hydrous aluminum silicate [Al₂Si₂O₅(OH)₄]. Kaolinite is produced by the weathering of granite.

Karst - A type of landform with limestone bedrock and dominated by geomorphic features created from solution chemical weathering.

Karst Water - Water rich in calcium and/or magnesium because it has flowed over limestone or dolomite deposits. Karst water is often associated with springs.

Katabatic Wind - Any wind blowing down the slope of a mountain or off large glacial ice sheets caused by the gravitational drainage of cold, dense air. These winds are usually strong and are more frequent at night.

Katafront - A condition where warm air descends along the surface of a front (usually a cold front). The sinking warm air inhibits the development of clouds and precipitation. This type of weak frontal activity often produces a shallow band of stratus clouds with little or no precipitation. Associated with mid-latitude cyclones and cyclogenesis.  Compare with anafront.

Kelvin Scale - Common scale used in science and engineering for measuring temperature. On this scale, absolute zero is 0 Kelvin, water boils at 373.15 Kelvin, and freezes at 273.15 Kelvin. One of the seven base measurement units used in the International System of Units (SI). Compare with Celsius and Fahrenheit temperature scales.

Kelvin Wave - A low-frequency gravity wave found in our planet's atmosphere or ocean that moves in one direction.  For Kelvin waves to form three conditions are needed: 1) the stable stratification of a fluid medium (atmosphere or water or ocean) for maintaining a gravitational oscillation, 2) a significant force generated by the Coriolis effect, and 3) the presence of a vertical boundary or the equator. In the Pacific Ocean, Kelvin Waves begin deep within the western equatorial Pacific and move to the ocean surface somewhere in the east. Pacific Ocean Kelvin Waves are used to forecast the start of an El Niño event.

Kettle Hole - Depression found in glacial deposits. Kettle holes are created when a piece of ice from a retreating glacier becomes embedded in soft glacial till or glacial drift deposits. Many are filled with water to form a small lake or pond. 

Kettle Moraine - An extensive area of glaciofluvial moraine deposits that has very uneven terrain and a number of kames and kettle holes found on it.

Keystone Species - A species that interacts with a relatively large number of other species in a community. Because of the interactions, the removal of this species can cause widespread changes to community structure. Compare with immigrant species, indicator species, and native species.

Kilocalorie (Kcal) - Unit of energy equal to 1,000 calories.

Kilopascal (kPa) - An International System of Units unit of measurement for quantifying force. Used to measure atmospheric pressure. Equal to one newton over an area of one square meter. Equivalent to 10,000 dynes per square centimeter or 1,000 Pascals.

Kilowatt (kW) - Unit of electrical power equal to 1,000 Watts.

Kimberlite - A type of igneous rock containing the minerals mica, olivine, and some times diamonds. Kimberlite occurs in the Earth's crust as vertical carrot-shaped structures that formed under high pressure and temperature within the mantle.

Kinetic Energy - The energy that an object or substance possesses due to motion.

Kingdom - The topmost level of the common hierarchical system used to classify life. Five kingdoms of life are recognized: Monera, Protista, Fungi, Animalia, and Plantae.

Kirchhoff's Law - This physical law suggests that good emitters of electromagnetic radiation are also good absorbers (absorption) of radiation at specific wavelength bands. It also suggests that poor emitters (emission) of radiation are also poor absorbers of radiation at specific wavelength bands. 

Klippe - An outcrop of rock that has been separated from another adjacent mass of rock because of a fault. 

Knick - A term of German origin used to describe the area where the slope suddenly becomes steeper between an isolated hill (inselberg) and the surrounding plain (pediment) where it is found.

Knickpoint (British spelling) - See nickpoint.

Knob and Kettle - A term commonly used in the United States to describe a glacially influenced landscape containing kames and kettle moraines. 

Knoll - A term commonly used to describe a small, round hill.

Knot - Nautical term used to describe the speed of movement. One knot is equal to 1.15078 miles per hour or 1.852 kilometers per hour. 

Koniology - A field of science that studies airborne dust, pollen, germs, and other airborne substances and their influence on other things. Also spelled coniology.

Köppen A: Tropical Moist Climates - Major category in the Köppen Climate Classification system. Locations classified as Köppen A have very warm climates and receive high quantities of precipitation. Köppen A climates are found in the tropics. The primary distinguishing characteristic of these climates is that all months have average temperatures above 18°C (64°F).

Köppen B: Dry Climates -  Major category in the Köppen Climate Classification system. Locations classified as Köppen B have climates have little precipitation during most of the year. Further, potential water losses from evaporation and transpiration greatly exceed the atmospheric input of precipitation.

Köppen C: Moist Mid-latitude Climates with Mild Winters - Major category in the Köppen Climate Classification system. Locations classified as Köppen C have warm-to-hot summers and mild winters. The primary distinguishing characteristic of these climates is that the coldest month has an average temperature between 18°C (64°F) and -3°C (27°F).

Köppen Climate Classification - A system that uses monthly precipitation and temperature data, and total annual precipitation data to classify a location's climate into one of five main categories: Tropical Moist Climates (A); Dry Climates (B); Moist Mid-latitude Climates with Mild Winters; (C) Moist Mid-Latitude Climates with Cold Winters (D); and Polar Climates (E). These categories are further divided into a number of subcategories. First developed in 1918 by the German biologist W. Köppen, this system has undergone several modifications.

Köppen D: Moist Mid-Latitude Climates with Cold Winters - Major category in the Köppen Climate Classification system. Locations classified as Köppen D have summer temperatures that are warm, and winters are cold. The primary distinguishing characteristic of these climates is that the average temperature of the warmest month exceeds 10°C (50°F), and the average temperature of the coldest month is below -3°C (27°F).

Köppen E: Polar Climates - Major category in the Köppen Climate Classification system. Locations classified as Köppen E have climates with very cold winters and summers, with no real summer season. The primary distinguishing characteristic of these climates is that the warmest month has an average temperature below 10°C (50°F).

Köppen H: Highland Climates - Major category in the Köppen Climate Classification system. Locations classified as Köppen H have climates strongly influenced by altitude.  As a result, the climate of such locations is very different from that of places at low elevations at similar latitudes.

Krotovina - An animal-created soil tunnel that has been infilled with some other type of sediment. 

Kurtosis - A statistical measure of the shape of data relative to the normal distribution. This measure varies from being leptokurtic (a distribution that has a more peaked shape) to mesokurtic (a properly shaped distribution) to platykurtic (a distribution that has a more flat shape) when graphed in a histogram. Also see skewness.

Kyoto Protocol - Is an international agreement associated with the United Nations Framework on Climate Change, aimed at mitigating human-caused climate change. This agreement achieves its goals by having signing nations reduce their atmospheric emissions of greenhouse gases on a specific agreed timeline. The Kyoto Protocol was initially adopted on December 11, 1997, in Kyoto, Japan, and its recommendations came into force on February 16, 2005. By September 2011, 191 nations had signed and ratified the agreement, with the United States as the major holdout. Canada renounced the agreement in December 2011.