I believe the Leviathan is a very distinct creature of the Bible and different to the usual 'sea monster', which I believe was a Nile crocodile. The Leviathan had many characteristics that do not fit a crocodile or any other animal.
If the ancient Hebrews had a specific name for their underwater volcano monster, other civilisations will also have named their respective volcano monsters.....and maybe the fear and zoomophism of them was something everyone in the volcanic Holy Land had in common. Maybe the stories of them started in one civilisation and were passed down into another.
One sea monster, which is described as mythological when it might in fact be fabled, is the Lernaean Hydra.
Here is a depiction of Lernaean Hydra...
and a depiction of the Leviathan....
It ravaged the country of Lernae near Argos, and dwelt in a swamp near the well of Amymone. However, with the assistance of his faithful servant Iolaus, he burned away the heads of the hydra, and buried the ninth or immortal one under a huge rock.
Statius, Thebaid 2. 375 ff (trans. Mozley) (Roman epic C1st A.D.) :
"The marsh of Lerna and the burnt Hydra’s heat makes warm the depths of those unrighteous waters."
The Hydra had the body of a serpent and many heads (the number of heads deviates from five up to one hundred there are many versions but generally nine is accepted as standard), of which one could never be harmed by any weapon. Also the stench from the Hydra's breath was enough to kill man or beast. When it emerged from the swamp it would attack herds of cattle and local villagers, devouring them with its numerous heads. It totally terrorized the vicinity for many years.That's enough of Hydra for now but I hope you can see the traits of an underwater gas leaking volcano. The herds were attacked by gas leaks, which is very reminiscent of the first born deaths in Exodus and the deaths in Job. The inability to kill it with weapons also aligns it with the Leviathan.
CHIMAERA (Chimaira), a fire-breathing monster, which, according to the Homeric poems, was of divine origin. She was brought up by Amisodarus, king of Caria, and afterwards made great havoc in all the country around and among men. The origin of the notion of this fire-breathing monster must probably be sought for in the volcano of the name of Chimaera near Phaselis, in Lycia (Plin. H. N. ii. 106, v. 27; Mela. i. 15), or in the volcanic valley near the Cragus (Strab. xiv. p. 665, &c.), which is described as the scene of the events connected with the Chimaera.Please see the link above for many examples of how ancient people used many animal names to describe just one nameless 'monster'...something they simply didn't recognise.
TYPHON (TYPHAON, TYPHOEUS), in Greek mythology, youngest son of Gaea and Tartarus. He is described as a grisly monster with a hundred dragons' heads, who was conquered and cast into Tartarus by Zeus. In other accounts, he is confined in the land of the Arimi in Cilicia (Iliad, ii. 783) or under Etna (Aeschylus, P.V. 370) or in other volcanic regions, where he is the cause of eruptions. Typhon is thus the personification of volcanic forces. Amongst his children by Echidna are Cerberus, the Lernaean hydra, and the Chimaera.From this...
As a volcano-daimon, Typhoeus hurled red-hot rocks at the sky and storms of fire boiled from his mouth.From this...
Typhon had frightful features and enormous powers. Soon, he attacked the home of the gods, flaming rocks at it, hissing, screaming and gushing mighty streams of fire from his mouth.
So, there seems to be a whole family of volcano monsters that instead of being described as myths should be described as fables because there is truth behind the tale...or should I say tail? And these are just the Hebrew one and the Greek ones. Apparently there is an Ethiopian one too...another day.
When the Leviathan is hungry, reports R. Dimi in the name of R. Johanan, he sends forth from his mouth a heat so great as to make all the waters of the deep boil, and if he would put his head into Paradise no living creature could endure the odor of him (ib.). His abode is the Mediterranean Sea; and the waters of the Jordan fall into his mouth (Bek. 55b; B. B. l.c.).
One thing is for sure, these monsters had breath that could kill.
PLEASE NOW READ MY EARLIER POST ON THE LEVIATHAN.