# What made the loud unidentified sounds recorded by NOAA's Pacific hydrophones in the 1990s? · Bloop and NOAA's unexplained ocean sounds > Four answers have been proposed. All of them are natural geophysical or cryogenic sounds (icequakes, grounding icebergs, volcanic eruptions… leads, with… Source: https://mysteriesdept.com/mysteries/noaa-ocean-sounds/questions/QST0D9C7CA41BJB/what-made-the-loud-unidentified-sounds-recorded-by-noaas Publisher: Mysteries Department Licence: CC BY 4.0 (credit Mysteries Department and link the page) Updated: 2026-10-26T11:58:17+00:00 --- **0** # What made the loud unidentified sounds recorded by NOAA's Pacific hydrophones in the 1990s? Asked 26 Oct 2026 by [**apollo** ](https://mysteriesdept.com/u/apollo)·4 answers·0·0 following **Most likely: all of them are natural geophysical or cryogenic sounds (icequakes, grounding icebergs, volcanic eruptions…** Ahead on the evidence, not yet confirmed. It needs two reviews to be accepted. ## Where it stands Four answers have been proposed. All of them are natural geophysical or cryogenic sounds (icequakes, grounding icebergs, volcanic eruptions… leads, with evidence 4 for, 1 against: partly supported by its tests. Three are still possible. Of the three narrower questions under it, none is answered yet. ## Why it matters The sounds were famous because they were unexplained, and the explanations now given rest on NOAA's own comparison of spectrograms and bearings rather than on published analyses of the original data⁠[[1]](https://mysteriesdept.com/sources/SRC0D9C70TY0F01/acoustics-monitoring-program-icequakes-bloop)⁠[[2]](https://mysteriesdept.com/sources/SRC0D9C712R2AJY/acoustics-monitoring-program-upsweep). Whether the ice attributions hold is also a question about how much a single spectrogram and a bearing can prove, which matters for every acoustic anomaly that follows. ## Answers 4 [**All of them are natural geophysical or cryogenic sounds (icequakes, grounding icebergs, volcanic eruptions…** ](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/answers/ANS0D9C7DH635Z3/all-of-them-are-natural-geophysical-or-cryogenic-sounds) Partly supported by its tests Evidence: 4 for, 1 against Most likely [**At least one of the sounds came from human activity (military exercises, ships, winches or other machinery).** ](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/answers/ANS0D9C7FZA5QEB/at-least-one-of-the-sounds-came-from-human-activity-military) Failed a test; not refuted outright Evidence: 2 against Disputed [**At least one of the sounds, most often the Bloop, was made by a large animal, known or unknown.** ](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/answers/ANS0D9C7F024MPX/at-least-one-of-the-sounds-most-often-the-bloop-was-made-by) Failed a test; not refuted outright Evidence: 1 for, 2 against Disputed [**None of these.** ](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/answers/ANS0D9C7GPR0Q8X/none-of-these) Not tested enough to call either way Evidence: none yet Still possible ## History 1. 2002[CNN puts forward: at least one of the sounds, most often the Bloop, was made by a large animal, known or unknown.](https://mysteriesdept.com/sources/SRC0D9C75Q645CK/tuning-in-to-a-deep-sea-monster) 1. 2002[Talandier et al.: ross Sea icebergs were recorded as far away as French Polynesia around the same years.](https://mysteriesdept.com/sources/SRC0D9C748A3W90/long-range-detection-of-hydroacoustic-signals-from-large)For: All of them are natural geophysical or cryogenic sounds (icequakes, grounding icebergs, volcanic eruptions… 1. 2002[CNN: the Bloop was far louder than any known animal; Lobel doubted cephalopods could make such a sound.](https://mysteriesdept.com/sources/SRC0D9C75Q645CK/tuning-in-to-a-deep-sea-monster)Against: At least one of the sounds, most often the Bloop, was made by a large animal, known or unknown. 1. 2002[CNN: the Bloop's rising frequency reminded biologists of animal calls.](https://mysteriesdept.com/sources/SRC0D9C75Q645CK/tuning-in-to-a-deep-sea-monster)For: At least one of the sounds, most often the Bloop, was made by a large animal, known or unknown. 1. 2005[Chapp et al.: ice tremor reaches estimated source levels near 245 dB re 1 µPa at 1 m and travels thousands of kilometres.](https://mysteriesdept.com/sources/SRC0D9C740G37ZY/sound-channel-observations-of-ice-generated-tremor-in-the)For: All of them are natural geophysical or cryogenic sounds (icequakes, grounding icebergs, volcanic eruptions… 1. 2014[Matsumoto et al.: antarctic icebergs are a major natural sound source heard at mid and equatorial latitudes, with seasonal…](https://mysteriesdept.com/sources/SRC0D9C73RP5QGT/antarctic-icebergs-a-significant-natural-ocean-sound-source)For: All of them are natural geophysical or cryogenic sounds (icequakes, grounding icebergs, volcanic eruptions… 1. 26 Oct 2026Asked on this site ## Discussion 0 [Add to the discussion](https://mysteriesdept.com/signin?next=/mysteries/noaa-ocean-sounds/questions/QST0D9C7CA41BJB/what-made-the-loud-unidentified-sounds-recorded-by-noaas%23discussion) Help with this question [ **Propose an answer** Something the evidence could support or rule out ] [ **Propose an answer** Something the evidence could support or rule out ](https://mysteriesdept.com/signin?next=/mysteries/noaa-ocean-sounds/questions/QST0D9C7CA41BJB/what-made-the-loud-unidentified-sounds-recorded-by-noaas%23add-answer) [ **Add evidence** A result for or against an answer ] [ **Add evidence** A result for or against an answer ](https://mysteriesdept.com/signin?next=/mysteries/noaa-ocean-sounds/questions/QST0D9C7CA41BJB/what-made-the-loud-unidentified-sounds-recorded-by-noaas%23add-evidence) [ **Ask a sub-question** A smaller question that would help settle this one ] [ **Ask a sub-question** A smaller question that would help settle this one ](https://mysteriesdept.com/signin?next=/mysteries/noaa-ocean-sounds/questions/QST0D9C7CA41BJB/what-made-the-loud-unidentified-sounds-recorded-by-noaas%23add-question) [ **Add a source** A paper, archive record or image ] [ **Add a source** A paper, archive record or image ](https://mysteriesdept.com/signin?next=/mysteries/noaa-ocean-sounds/questions/QST0D9C7CA41BJB/what-made-the-loud-unidentified-sounds-recorded-by-noaas%23add-source) Where it fits Bloop and NOAA's unexplained ocean sounds **What made the loud unidentified sounds recorded by NOAA's Pacific hydrophones in the 1990s?** Key question · you're here [Was the Bloop an icequake, and from which iceberg?](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/questions/QST0D9C7CHY4R4M/was-the-bloop-an-icequake-and-from-which-iceberg)Most likely · the Bloop was one or more icequakes from a large iceberg cracking somewhere between Bransfield Strait and the… [Were Train, Slow Down and Julia made by icebergs grounding on the seafloor?](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/questions/QST0D9C7D1J3NMQ/were-train-slow-down-and-julia-made-by-icebergs-grounding-on)Most likely · all three were produced by large icebergs settling on or dragging across the seafloor [Where did Whistle come from?](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/questions/QST0D9C7D9C6V99/where-did-whistle-come-from)Most likely · whistle was an eruption signal from a distant submarine arc volcano [ Ask a question under this one ]