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Ephemeral things (from Greek εφήμερος – ephemeros, literally "lasting only one day") are transitory, existing only briefly. Typically the term is used to describe objects found in nature, although it can describe a wide range of things.
An ephemeral waterbody is a wetland, spring, stream, river, pond or lake that only exists for a short period following precipitation or snowmelt. They are not the same as intermittent or seasonal waterbodies, which exist for longer periods, but not all year round.
Examples of ephemeral streams are the Luni river in Rajasthan, India, Ugab River in Southern Africa, and a number of small ephemeral watercourses that drain Talak in northern Niger. Other notable ephemeral rivers include the Todd River and Sandover River in Central Australia as well as the Son River, Batha River and the Trabancos River.
Any endorheic basin, or closed basin, that contains a playa or dry lake at its drainage lowpoint can become an ephemeral lake. Examples include Lake Carnegie in Western Australia, Lake Cowal in New South Wales, Mystic Lake and Rogers Lake in California, and Sevier Lake in Utah. Even the driest and lowest place in North America, Death Valley (more specifically Badwater Basin), became flooded with a short-lived ephemeral lake in the spring of 2005.
There are also ephemeral islands such as Banua Wuhu and Home Reef. These islands appear when volcanic activity increases their height above sea level, but disappear over the course of several years due to wave erosion. Bassas da India, on the other hand, is a near-sea level island that appears only at low tide.
Many plants are adapted to an ephemeral lifestyle, in which they spend most of the year or longer as seeds before conditions are right for a brief period of growth and reproduction. The spring ephemeral plant mouse-ear cress is a well-known example.
Ephemeral can also be used as an adjective to refer to a fast-deteriorating importance or temporary nature of an object to a person. Brands are notoriously ephemeral assets, magazine publishing was once much more ephemeral than it is today, as was television programming.
A number of art forms can be considered ephemeral because of their temporary nature. Early land art and all sand sculptures, ice sculptures and chalk drawings on footpaths are examples of ephemeral art. G. Augustine Lynas and Duthain Dealbh create ephemeral sculptures.
Often happiness is described as being ephemeral, as one does not find it to be a permanent state, within the scope of human lives. There are always varying shades of happiness and disappointment.
In computer networking technology, an ephemeral port is a TCP, UDP or SCTP port which is dynamically assigned to a client application for a short period of time (the duration of time the application is running). This is in contrast to the "well known" ports which are typically statically assigned to a specific application or service.
Other uses also include:
- Ephemeral film, a film made by a particular sponsor for a specific purpose other than as a work of art
- Ephemeral key, a cryptographic key generated for each execution of a key establishment process
- Ephemeral (EP), a 2009 EP by post-metal band Pelican
- Ephemeral, a 1997 album by Synæsthesia (band)
- Ephemeral data structures, the opposite term for persistent data structures.
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