In the mid-6th century, legend has it, St Brendan set off from Ireland with a currach-load of monks on a mission to find the Isle of the Blessed. The Irish like to think that his Atlantic odyssey took him to Newfoundland before the Vikings; what seems more probable, if you believe the medieval account, is that it brought him close to the shores of Iceland where he passed a mountainous island with ‘a great smoke issuing from its summit’ and ‘flames shooting up into the sky’.

If there were any doubts that what is meant here is a volcano, they would be dispelled by the drawing in the margin of the version of the Navigatio Sancti Brendani Abbatis currently on show at the Bodleian Libraries. This 14th-century manuscript is not the oldest object in the Bodleian’s new exhibition Volcanoes. That honour belongs to a carbonised scrap of papyrus from a private library in Herculaneum buried during the great AD 79 eruption of Vesuvius described by the 17-year-old Pliny the Younger, who survived it. His less fortunate uncle, Pliny the Elder, who bequeathed the name ‘Plinian’ to the particular sort of violent ash cloud in which he perished, is remembered in the show by a Renaissance manuscript of one of his letters.

But this is not an antiquarian exhibition. Its curator is David Pyle, professor of earth sciences at the University of Oxford, and its thesis is that marshalling historical evidence of past explosions is the best way of predicting future ones. When dealing with capricious geological phenomena measured in hundreds, if not hundreds of thousands, of years, the further back in history you can go the better.

Volcanoes have fascinated scientific minds since the early Greek-Sicilian philosopher Empedocles concluded from studying Etna that rather than clinging to a rock, as Boy George would have it, humanity was sitting on a hot potato. The active volcanoes of Magna Graecia and the Cyclades — the currently peaceable tourist island of Santorini blew its top in 197 BC and again in AD 46 — provided the ancient Greeks and Romans with plenty of evidence of this fact. But it wasn’t until the Age of Exploration that interest in vulcanology really sparked.

Like St Brendan, most early explorers of volcanoes seem to have been priests; perhaps they felt that closeness to Earth’s molten core would bring them ‘nearer, my God, to thee’. Whatever the reason, the early annals of vulcanology are full of inquisitive monks on scientific missions to get to the fiery bottom of creation. In 1664 the German Jesuit polymath Athanasius Kircher published his pioneering researches into the workings of Vesuvius, Etna and Stromboli in the treatise Mundus Subterraneus; illustrated with some of the first cutaway diagrams, it established that the phenomenon of ‘rebelching mountains’ originated ‘in the very in-most privy-Chambers and retiring places of the Earth’. Kircher wasn’t inquisitive enough to test the theory in person, unlike the Spanish Dominican Fray Blas de Castillo who, in 1538, had himself lowered down into the Nicaraguan volcano Masaya in a basket with a hammer, a crucifix and a flagon of wine. His motivation was monetary as well as scientific: it was hoped that the red-hot magma might contain precious metals, but it cooled disappointingly into worthless scoria.

In the 1790s, the Italian priest Lazzaro Spallanzani, chair of natural history at the University of Pavia, conducted some more sophisticated experiments on volcanic rock samples brought back from his travels in southern Italy, subjecting them to intense heat in a smelting furnace before extracting a liquid that contained hydrochloric acid, as he discovered by testing it on his tongue. But the most diligent 18th-century student of Italian volcanoes was not a priest, but a Scottish diplomat. Posted to Naples in 1764 as Envoy Extraordinary to the Kingdom of the Two Sicilies, the dilettante geologist William Hamilton became so fascinated by the activity of Vesuvius, then in one of its excitable phases, that he stayed in his poorly paid post for 37 years partly in order to monitor it. His two volumes of observations compiled for the Royal Society of London in 1776 and 1779, for which he commissioned vivid on-the-spot illustrations from the young Italian artist Pietro Fabris, are some of the first blow-by-blow accounts of volcanic activity, and the most sumptuously illustrated. Whether Hamilton’s passion was shared by his wife Emma is not recorded, but it could explain his laid-back attitude to her affair with Nelson — next to a volcano, she was not such hot stuff.

With the invention of the camera, volcanic imagery becomes noticeably duller. Compared with the red-hot drama of Fabris’s paintings, an early slide of Vesuvius erupting in April 1872 is all smoke and no fire. The post-apocalyptic images of the aftermath of the 1902 eruption of the Soufrière Saint Vincent recorded by the aptly named volcano photographer Tempest Anderson pale by comparison with J.M.W. Turner’s pyrotechnic vision of the same volcano erupting in 1812, painted from a borrowed sketch and his imagination. Turner’s painting is not in the show, but its lurid palette is easily matched by William Ashcroft’s watercolour records of the freak series of blood-orange sunsets seen over the Thames at Chelsea in November 1883, three months after the spectacular eruption of Krakatoa.

The worrying thing about volcanic eruptions, for those of us living on geologically stable islands, is how far-reaching their effects can be. When a volcano throws up a plume of ash and gas 12 miles into the air, the environmental repercussions are global. The fallout from the eruption of Krakatoa’s sister volcano Tambora in April 1815, witnessed by Stamford Raffles as governor of Java, caused widespread crop failures in the ‘year without a summer’ that followed, when the Swiss were reportedly reduced to eating cats. But even volcanic clouds have silver linings. Stuck indoors that rainy summer while on holiday in Geneva, Byron, Shelley and the then Mary Wollstonecraft Godwin fended off boredom by making up ghost stories. An original draft of Mary Shelley’s Frankenstein, published two years later, is in the exhibition.

Pyle makes no attempt in his catalogue to disguise the fact that vulcanology is not a precise science; even with modern advances in monitoring equipment the ground beneath our feet remains rocky. The bad news is that the most violent eruptions tend to come from volcanoes that have lain doggo for centuries, quietly accumulating magma. The best we can do is ‘use measurements of how the Earth’s gravity and magnetic field change across the surface of the planet to get a fuzzy idea of what might be happening at depth’.

It’s hardly reassuring. Better keep the cat well fed and the Gothic novel ideas on ice.