blowhole

1. An opening or one of a pair of openings for breathing, located on the top of the head of cetaceans, such as whales and dolphins. The blowhole is opened by muscles upon surfacing and closed by the pressure of water upon diving.
2. A hole in ice to which aquatic mammals, such as dolphins, come to breathe.
3. A vent to permit the escape of air or other gas.

A crack in the top of a cliff through which air and sea water blow. The blowhole is fed from the seaward end via joints and tunnels.

The anterior nares of whales and dolphins.

The noun has 2 meanings:

Meaning #1: the spiracle of a cetacean located far back on the skull

Meaning #2: a hole for the escape of gas or air
  Synonyms: vent, venthole

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Alofaaga Blowholes

The blowhole of Monks' Cave, a sea cave near Aberystwyth

In geology, a blowhole is formed as caves grow landwards and upwards into vertical shafts and expose themselves towards the surface , which can result in quite spectacular blasts of water from the top of the blowhole if the geometry of the cave and blowhole and state of the weather are appropriate. The Kiama Blowhole (Kiama, New South Wales, Australia) is believed to be the world's largest blowhole. [1]

A blowhole is also the name of a rare geologic feature in which air is either blown out or sucked into a small hole at the surface due to pressure differences between a closed underground cavern system and the surface. The blowholes of Wupatki National Monument are an example of such a phenomenon. It is estimated that the closed underground passages have a volume of at least seven billion cubic feet. Wind speeds can approach 30 miles per hour.^[1]

Notes

1. ^ Investigations of the Wupatki Blowhole system

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