SLOPE FAILURE TYPES:

Rotational slide

rotational

SLOPE FAILURE NAME:

Rotational slide

DEFINITION:

Consists of a movement of rock or debris, about an axis that is parallel to the slope contours, involving shear displacement along a concave upward – curving failure (VARNES, 1978).

MAIN CHARACTERISTICS:

These failures tend to be deep, and involve rock and overlaying debris as well. They can develop over various areas, from very large cliff areas to tiny, metre sized rock scars.

Rotational slides often develop in areas of interbedded strong and weaker material, especially basalts and palaeosoils at the Giant’s Causeway.

Differences between rotational and translational slides are sometimes very difficult to establish. Many times rotational and translational slides have the same causes and associated hazards, and can occur under the same weather conditions. In general, if a slide did not involve the substratum, but only shallow debris, we have tended to define it as “translational”.

Accumulated debris is normally seen below the landslide scar, and often it is not significantly deformed. This characteristic is not always accomplished in Giant’s Causeway, as slided rocks use to crack and bounce once they start moving. At the Causeway, however, well – jointed basalts at the top of the failure can roll or bounce a considerable distance down, creating a complex failure.

CAUSES:

Severe moisturing and filling on debris and substratum, using cracks. Undercutting can also be a determinant unstabilization factor and origin rotational landslides.

AREAS PRONE TO FAILURE:

Any area where there is an alternation between strong/weak or permeable/impermeable layers. This can happen in places where interlayered old soils are present.

The Amphitheatre, the eastern part of Portnaboe and Great Stookan are potential areas for these landslides.

OCCURRENCE:

During or after long duration rainfall.

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