Scientific Background and Goals

Storegga Slide Coring Cruise

Written by Michele Hatton
Educator & Florida State undergraduate geology student

What is the Storegga Slide?

The Storegga Slide is a massive submarine landslide that occurred off the coast of Norway. Emplaced through a series of geological events that probably culminated about 8,200 years ago, the slide covers over 100,000 km2 of seafloor (an area roughly equal to the size of Scotland). The slide transported huge amounts of sediment, and probably triggered tsunami activity in the northern Atlantic Ocean.

What was the goal of the cruise?

The primary objective of the Storegga Slide Coring Cruise (KN179-03) was to obtain sediment cores from different parts of the Storegga Slide, including the sole of the slide, the headwall, the flanks, and the undisturbed seafloor adjacent to the slide. The Storegga Slide has been surveyed numerous times; however, this was the first expedition to target pore waters for analysis.

During KN179-03, 178 water samples were extracted from 32 cores. Also collected were 27 core-top water samples. The cores were obtained so scientists could perform geochemical analysis on extracted pore waters and sedimentological studies of the core sediment. Pore waters were analyzed for concentrations of sulfate, methane, and chlorine in a mobile laboratory aboard the ship.

How can scientists explore what caused the Storegga Slide?

The prevailing argument for the cause of the submarine landslide is a gas-venting scenario. Gas hydrates are very small, solid crystalline structures, similar to ice, that are buried within some seafloor sediments. The structure of the hydrates permits them to trap a molecule of gas. In marine environments, this gas is usually methane (CH4).

When present, gas hydrates may either stabilize or destabilize a submarine slope, depending on conditions. As they form, hydrates fill the pore spaces between slope sediments, strengthening the slope and making it less likely to fail. However, when hydrates dissociate, they weaken the slope and can trigger landslides.

Scientists envision that the Storegga Slide was caused by the dissociation of gas hydrates, due perhaps to thermal warming of deep ocean waters or to a large earthquake. In this scenario, sediment that was once gas-rich would have become gas-poor. By determining fluid and gas concentrations in gas-sensitive pore waters collected from different parts of the slide, it is possible to delineate which areas of the slide are gas-rich and which are gas-poor. In addition, sedimentological data collected during the cruise provide information on the shear strength of the geological material in different parts of the slide. Shear strength is a characteristic of sediment and rock that tells scientists how likely a material is to fail, or be involved in a geological event like a landslide.