"I have plenty of theories."
Mulder, F.W. in the “The X-Files” (1993)
Summer is traditionally Silly Season, when newspapers publish strange stories about aliens and monsters again and again to bridge holiday time - and so will July on "History of Geology" be dedicated to frivolous science stories...
In 2001 the Italian geologist Luigi Piccardi presented during the Earth Systems Processes meeting in Edinburgh a hypothesis explaining the supposed appearance of the sea/lake monster "Nessie" as a result of geologic forces.
According to Piccardi's idea the historic description of the monster - appearing on the surface with great (earth)shakes and rumours - could be associated with bubbles emanating from the bottom of the Scottish lake of Loch Ness in response of seismic activity along the Great Glen fault system, passing below the lake.
In an interview published June 28 in the Italian newspaper "La Repubblica" Piccardi explains:
"There are various effects on the surface of the water that can be related to the activity of the fault.. If we consider the terms used by Adamnan, the beast appears and disappears with great shakes. I think it's an obvious description of what really happened… We know that this was a period [1920-1930, a period characterized by many reported sightings of Nessie] with increased activity of the fault, in reality people have seen the effects of the earthquakes on the water."
According to the biography by Adamnan of Saint Columba ("Vita Sancti Columbae", written in the year 690) the scene described by Piccardi happened in 565 A.D. Trying to cross the river Ness the saint is attacked by a beast - but Columba implores the protection of god and the monster promptly disappears. The original text however is very vague and gives no detailed description of the event, it states only that it was an "unknown beast" and it approached with the mouth wide open and a loud roar (Piccardi's interview and interpretation of the historic source prompted a detailed rebuttal by Italian zoologists). The mention that the beast was of unknown origin makes it appear as unique event, so seemingly no monster tradition existed previously (and as plesiosaur, Nessie had to come to the surface to breathe and should be spotted more often). For Adamnan obviously Nessie was much less of interest than the ability of Saint Columba to tame beasts and demons - an important qualification for early missionaries - so it is possible he added this encounter to make St. Colombian´s legend bigger than real life.
Even if this anecdote is granted for real, the vague description doesn't really support any proposed scenario, neither bubbles emanating from the river or a presumed lake monster. A surviving plesiosaur in Loch Ness can more reasonable be explained by a combination of hoaxes, misidentification of common animals and promotion for tourists - a long tradition of research on the lake has never delivered even a clue for the possible existence of any larger animal in the Loch.
Fig.1. Title page of Jules Verne's 1867 edition of "Voyage au centre de la Terre" with a vignette by Edouard Riou, depicting a fierce battle between pterodactyls, a Plesiosaurus and a Mosasaurus, such images mark the first appearance of these Nessie-like creatures in popular fiction (image in public domain).
Not only biological constrains, also the geology don't seems to support the existence of an earthshaking monster in Loch Ness. Common earthquakes from the Loch Ness area range between magnitude 3 to 4, larger events were recorded only in 1816, 1888, 1890 and 1901. These earthquakes don't coincide with the years of supposed increased activity of Nessie (like 1933). Even the largest Scottish earthquakes were anyway too weak to cause any observable effects on the surface of Loch Ness (curiously the great earthquake of Lisbon in 1755 generated waves on Loch Ness, but no Nessie sighting is reported for this year).
Piccardi himself sees the value of his hypothesis more in the possibility to make geologists aware of the geological origins of some myths, as to propose verifiable cryptozoology.
PICCARDI, L. (2001): Seismotectonic Origins of the Monster of Loch Ness. Poster Session G5. Earth System Processes - Global Meeting (June 24-28, 2001)