Methane hydrate

Methane hydrate is a cage-like solid in which water molecules surround and trap methane. In the novel, it is at once an immense, alluring energy resource and a hidden support for the seabed: hydrate layers bind continental slopes together, so their destabilization threatens to turn a deep-ocean process into a landslide and tsunami. Its importance lies in that double role. The same material that promises fuel can also be a geological time bomb.

Formation and Seabed Setting

Continental shelves are the relatively shallow underwater continuations of the continents, generally no more than two hundred metres deep. Beyond them, the seafloor descends along continental slopes toward the ocean basin. These deeper regions are difficult to observe directly, but they are where the novel places many hydrate deposits and the geological danger they pose.

Methane can form over millions of years as plants and animals decay, with bacteria playing a central part in the production of biogenic gas. At depths greater than about five hundred metres, cold water and high pressure can cause methane seeping through the seabed to become enclosed within solidifying structures of water molecules. The methane itself does not freeze; water forms cages around it, compressing large quantities of gas into a small volume. The required conditions are not confined to a single depth. Hydrates occur at depths of up to three thousand metres where organic-rich sediment accumulates, and they can also form in shallow polar waters if temperatures are sufficiently low.

The principal deposits described by Bohrmann lie on continental slopes, usually between five hundred and a thousand metres deep. Hydrates may be buried in rock or exposed on the seabed, while deeper sediment can contain pockets of methane that remains gaseous beneath the frozen layer. The hydrate acts as a lid over those pockets. More broadly, it acts as cement within the slope: remove it, and the seabed becomes porous and vulnerable to landslides. The material is therefore not merely a substance stored beneath the ocean floor; it is part of what holds that floor together.

Instability and the Release of Gas

The hydrate’s stability depends on the combination of low temperature and high pressure. Even a small change can matter. Bohrmann warns that at a depth of five hundred metres, a temperature increase of just one degree might destabilize the hydrate stock at that level. In one demonstration, hydrate recovered from eight hundred metres began dissociating halfway to the surface. By the time the samples reached the research vessel Sonne, much of the material was gone; the remaining pieces were plunged into liquid nitrogen to slow the process.

As hydrate dissociates, its water cages break down and methane escapes. The volume change makes the process particularly consequential: each cubic centimetre of hydrate can release 164 cubic centimetres of methane. The sample demonstration makes the transformation visible as a solid becomes sediment-specked water, while the escaping gas is the more consequential part of the change. On a seabed, dissociation can leave behind a weakened, porous structure and release gas into surrounding water and, potentially, the atmosphere.

The novel distinguishes ordinary methane seepage from the abnormal conditions discovered off the Norwegian continental slope. Methane plumes can arise where geological processes allow gas to escape from the seabed; currents can carry dissolved gas upward. But the highly concentrated plume detected there did not fit earlier data, and such conditions were unusual for the region. Bohrmann reports that hydrate layers in the area were sixty to a hundred metres thick, with vertical breaks through which gas had escaped for years. The high concentration of free gas, rather than the mere existence of seepage, indicated that the situation had become dangerous.

Readings from the research vessel Thorvaldson agreed with those taken elsewhere along the slope: the sea was saturated with methane, and large sections of hydrate had begun to destabilize. The stability field itself had not changed, leading the scientists to suspect processes deeper in the sediment than the worms could burrow. At first, the possibility that worms had triggered the change remained under consideration. Later discussion rejects the earlier assumption that the worms themselves were destabilizing the hydrate. The account thus moves from an unexplained geological anomaly to a more complicated distinction between the visible organisms and processes operating deeper below them.

Scientific Investigation and Economic Stakes

Methane hydrate attracts scientific interest because it is difficult to study in its natural setting and changes during recovery. The energy industry is drawn to the scale of the resource, while researchers are concerned about its instability and its structural role in the seabed. Bohrmann estimates that marine gas hydrates may contain twice as much burnable methane as all other known deposits of gas, oil, and coal combined. A hydrate ridge off the American coast is described as extending over 26,000 square kilometres and containing 35 gigatons of hydrate, an amount compared to one hundred times the natural gas used in the United States in a year. The broader estimate is more uncertain: marine deposits may hold over 10,000 gigatons of methane, while known coal, oil, and gas reserves together amount to barely 5,000 gigatons. Even extracting one per cent of the hydrate methane could, in Bohrmann’s account, double United States fuel reserves.

The scale of the resource sharpens the conflict between extraction and caution. Hydrates from an expedition had already begun to dissociate during their ascent, demonstrating how hard it is to bring the material to the surface intact. A temperature change could also destabilize deposits in place, while removing the hydrate would undermine the slope it supports. The prospect of abundant fuel therefore cannot be separated from the possibility that attempts to exploit it could release methane or contribute to seabed failure.

A pressure laboratory at the GEOMAR Centre offers a way to investigate hydrate behaviour without launching an expedition for every question. Its simulator cannot reproduce the seabed in full, but it allows researchers to vary pressure and temperature precisely and test general hypotheses. In one setup, conditions correspond to a depth of eight hundred metres; a two-metre layer of stable hydrate sits above a simulated pocket of gaseous methane heated from below. In the ocean, Bohrmann explains, the comparable hydrate layer might be twenty or thirty times thicker. The model makes the relationship between a sealing hydrate layer and trapped gas experimentally accessible, while also underscoring the limits of reproducing a vast and only partly observed environment.

From Blowout to Slope Collapse

The danger becomes immediate when the T. Rex video-guided grab is lowered to collect a seabed sample beneath the Sonne. This heavy, jawed sampler bites into sediment to retrieve material, but during the operation it penetrates more than twenty metres through the hydrate layer. Gas surges upward in a blowout, visible as an enormous bubble on the screen. The incident demonstrates how sampling a deposit can expose gas beneath it, turning an investigation into a hazardous disturbance.

The larger collapse follows a more extensive destabilization. Hydrates that had been transformed from stable fields and veins into porous, brittle material disintegrate across 150 kilometres of slope. As the methane escapes, it breaks through sediment and rock; the seabed rises and slides forward. Cubic kilometres of stone collapse, and debris falls onto further layers, helping reduce them to mud. One failure triggers another, until the movement spreads along the shelf margin.

The slide is described as a Storegga-scale event, with hundreds of kilometres of slope moving down by as much as 3,500 metres toward the abyssal plains east of Iceland. The displacement lowers sea level over a vast region and forces surrounding water outward in a travelling wave. Near the landslide, the wave is initially so low—scarcely a metre above the surface over an area of several thousand square kilometres—that it is hidden amid the storm. Farther along the coast, seabed topography and river mouths shape its destructive reach; the wave floods the Frisian Islands and races up the Elbe and Weser. Within an hour of the underwater avalanche, northern Europe’s offshore oil industry has ceased to exist, coastal towns have been ravaged or destroyed, and hundreds of thousands of people have died. The catastrophe gives geological scale to the novel’s central warning about hydrate: a material almost invisible to people at the surface can determine the stability of the world above it.