Peat landslide in Ireland impacts downstream river

A peat landslide that occurred in Ireland has probably highly impacted a river downstream.

Peat (or turf) is formed by the decomposition of organic material in wet environments like bogs or moors. In terms of mechanical behavior, peat is a unique soil with particular  properties. These include: 1) low shear strength, 2) reduced unit weight compared to typical soils; in fact, research suggests that its unit weight is similar to that of water (9.81kN/m³) and, 3) relatively high tensile strength which is associated with the fibers contained in the material. Once it is disturbed, landslides with long runouts can be triggered.

The extent of peat deposits is significant as it occupies 5%-8% of the Earth's surface and more than half of the world's wetlands. Nevertheless, its composition and behavior are highly dependent on the organic matter from which it consists and the surrounding environment that results in its formation (e.g., climate and humidity).

Peat failures are usually reported as bog bursts or peat slides and are characterized by quick soil movements that frequently occur after prolonged rainfalls. They are very common in northern regions of the United Kingdom and especially in Ireland. The extent of peat landslides varies with some being massive carrying thousands of the material's cubic meters. Such slides can cause a severe impact on local infrastructure and stream ecology.

On November 13, 2020, a large peat slide struck near Ballybofey, a small town located in County Donegal, Ireland. Moving downslope, the landslide transformed to a quick flow that traveled a great distance and impacted the Mourne Beg river. According to AGU, the initial failure probably started downslope and was followed by headscarp retrogression since the upper part of the slide lies in an extensional zone. The ground failure occurred near a wind farm facility that was under construction.

The Mourne Beg river accommodates a protected Salmon species therefore, its prosperity is essential. In November 2020, the UAF (Ulster Angling Federation) stated that the river may not recover from the landslide but the actual damage will be revealed in spring when its water supply will be higher. Nevertheless, according to a recent report, the river is apparently damaged and an investigation on the potential restoration schemes is ongoing. UAF also warned about the water pollution that the peat landslide has caused. "Needless to say this is a very significant pollution event, one of the largest in the history of Northern Ireland and Ireland and involving large acreages of bogland. It is one that will be difficult to reinstate," UAF, stated.

After the incident, Irish officials ensured people that there is no public risk associated with drinking water as the drainage of the impacted river had been suspended.

Two videos capturing the extent of the peat landslide can be found below.