thumb|A [[spectrogram of Bloop]]
Bloop was an ultra low frequency, high-amplitude underwater sound detected by the U.S. National Oceanic and Atmospheric Administration (NOAA) in 1997. was replaced by NOAA's description of the sound as being consistent with noises generated via non-tectonic cryoseisms originating from glacial movements such as ice calving, or through seabed gouging by ice.
Sound profile
The sound's source was roughly triangulated to , a remote point in the South Pacific Ocean west of the southern tip of South America. The sound was detected by the Equatorial Pacific Ocean autonomous hydrophone array,
According to the NOAA description, the sound "rose" in frequency over about one minute and was of sufficient amplitude to be heard on multiple sensors, at a range of over .
Ice quake origin
The NOAA Vents Program has attributed the sound to that of a large cryoseism (also known as an ice quake). Icequakes, caused by the fracturing and movement of large ice masses, can produce powerful low-frequency sounds that propagate over vast distances in water. This mechanism could explain the Bloop's wide detection range and distinct acoustic signature. As oceanographer Yunbo Xie explains, the alteration of waveforms from a detected sound "can also be caused by so-called angular frequency dependent radiation patterns associated with antisymmetric mode motion of the ice cover." Rubbing involves two or more areas of compacted glacial ice floes which are being forced together, inducing shear deformation at its edges and triggering horizontally-polarized shear waves, i. e. SH waves. In 2002, Fox was interviewed by David Wolman for an article in New Scientist, where he stated that he did not believe its origin was man-made, such as a submarine or bomb. Fox also stated that while the audio profile of Bloop does resemble that of a living creature, Wolman reported in his article the following: