Tsunami

A tsunami is a series of waves shaped when a body of water, such as an ocean, is rapidly displaced. Earthquakes, group movements above or below water, volcanic eruptions and other underwater explosions, landslides, large meteorite impacts and testing with nuclear weapons at sea all have the potential to produce a tsunami. The effects of a tsunami can range from imperceptible to devastating. The word tsunami comes from the Japanese words meaning harbor and wave. For the plural, one can either follow usual English practice and add an s, or use an invariable plural as in Japanese. The term was created by fishermen who returned to port to find the area neighboring their harbor devastated, although they had not been conscious of any wave in the open water. Tsunamis are general throughout Japanese history; approximately 195 events in Japan have been recorded.
A tsunami has a much smaller amplitude (wave height) offshore, and a very long wavelength, which is why they generally pass unobserved at sea, forming only a passing bulge in the ocean. Tsunami have been historically referred to as tidal waves because as they approach land, they take on the characteristics of a vicious onrushing tide rather than the sort of cresting waves that are formed by wind action upon the ocean. Since they are not really related to tides the term is considered misleading and its treatment is discouraged by oceanographers.

Populations

Populations are studied, in exacting, in a branch of ecology known as population biology, and in population genetics. In population dynamics, size, age and sex structure, mortality, reproductive behavior, and development of a population are studied. In biology, an isolated population denotes a breeding group whose members breed mostly or solely among themselves, usually as a result of physical isolation, although biologically they could breed with any members of the varieties. If there are several completely or nearly completely secluded populations in the global population of a taxon, these are called subpopulations. The Metapopulation is a network of subpopulations in a given area, where the individuals of the various subpopulations are able to cross dilapidated areas of the region. Biological dispersal is one of the key elements upsetting such populations; if dispersal is sufficiently low for a prolonged period of time, speciation is likely to be a consequence.
Population growth is varying in population over time. It also can be quantified as the change in the number of individuals in a population per piece time. The term population growth can technically refer to any species, but almost always refers to humans, and it often used easily for the more specific demographic term population growth rate, and is often used to refer specifically to the expansion of the population of the world.

River

A river is a natural waterway that transits water through a setting from higher to lower elevations. A river may have its basis in a spring, lake, from damp, boggy landscapes where the soil is waterlogged, from glacial melt, or from surface runoff of precipitation. Almost each and every one river is joined by other rivers and streams termed tributaries the highest of which are known as headwaters. Water may also begin from groundwater sources. Throughout the course of the river, the total volume transported downstream will often be a combination of the free water flow together with a important contribution flowing through sub-surface rocks and gravels that underlie the river and its floodplain. For many rivers in large valleys, this unseen component of flow may greatly go above the visible flow.
From their source, all rivers flow downhill, typically terminating in the sea or in a lake, through a confluence. In arid areas rivers sometimes end by losing water to desertion. River water may also infiltrate into the soil or pervious rock, where it becomes groundwater. Excessive abstraction of water for use in commerce, irrigation, etc., can also cause a river to dry before success its natural terminus.