swamp gas

English

Etymology

• (hydrogen sulfide): So called because it is often emitted from wetlands such as swamps as a result of anaerobic bacteria, and is responsible for their foul “rotten egg” odor.
• (ufology): An explanation given by then-skeptic J. Allen Hynek for an alleged UFO sighting in Michigan near Lake Huron in 1966.

Noun

swamp gas (uncountable)

1. (literally) gases emitted from a swamp

   Synonyms: bog gas, marsh gas, biogas

2. (inorganic chemistry, colloquial) hydrogen sulfide

   Synonym: rotten egg gas

3. (ufology, sarcastic) a skeptical explanation to debunk a UFO sighting that a believer regards as silly, illogical or disingenuous

   Synonyms: weather balloon, pelican