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Post Info TOPIC: Three Storegga Slides
Blobrana


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RE: Three Storegga Slides
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Title: The Holocene Storegga Slide tsunami in the United Kingdom
Authors: D.E. Smith, S. Shi, R.A. Cullingford, A.G. Dawson, S. Dawson, C.R. Firth, I.D.L. Foster, P.T. Fretwell, B.A. Haggart, L.K. Holloway, D. Long

All currently known sites in the United Kingdom with evidence for the Holocene Storegga Slide tsunami are described. Information on the altitude, distribution, stratigraphical context, age, particle size profile and microfossil characteristics of the deposits is presented. The tsunami involved a greater area than previously described, reaching a coastline over 600 km long. The ubiquitous sand layer which forms the main deposit associated with the event is shown to exhibit a consistent morphology and a particle size profile marked by fining-upwards sequences. An analysis of new and previously published radiocarbon dates indicates that from evidence in the United Kingdom, the event took place sometime around 7100 radiocarbon years BP (7900 calibrated years BP). A new isobase model for mainland Scotland and adjacent areas, providing a preliminary estimate of land uplift since the tsunami, is presented. The model estimates contemporary sea surface level offshore at 14 m below the present day mean high water spring tides. Tsunami sediment run-up is greatest in inlets, where it reaches at least 25 m on Shetland and at least 5 m along the mainland coastline to the south, and run-up of the tsunami would have exceeded these values. The tsunami sediments identified here are considered particularly valuable as a synchronous marker horizon.

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Another expert, Canadian geologist-geographer Edward Bryant said tsunamis had happened with greater frequency then modern science would like us to believe and no coastline was safe.
He had found signs of giant waves sweeping over 425 feet high headlands in southeast Australia, roaring down the US west coast and carving into the bedrock of the Scottish coastline north of Edinburgh.
Bryant, the head of geosciences at Woolongong University near Sydney, believed the famous St Andrews golf course was a tsunami deposit.
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Blobrana


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Palaeotsunami
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The east coast of Scotland was struck by a 70 feet (21 m) high tsunami around 6100 BC, during the Mesolithic period. The wave was caused by the massive underwater Storegga slide off Norway, which dates from around the same time. The tsunami even washed over some of the Shetland Islands. Tsunamite (the deposits left by a tsunami) dating from this event can be found at various locations around the coastal areas of Scotland, and are also a tourist feature in the Montrose Basin, where there is a thick layer of deposited sand about 0.6 metres thick.
In 2003, some geologists noticed that formerly frozen methane, beneath the ocean floor on the edge of the continental shelf off Norway, was weakening a vast section of land, not far from the place where the Storegga slide occurred. They found enough evidence to conclude that one day it will result in a huge landslide that will send tsunami waves down the east coast of Britain. Some believe it may happen sometime in the next 200 years.

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Blobrana


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Three Storegga Slides
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Title: Reconstructing the pattern and depth of flow onshore in a palaeotsunami from associated deposits.
Authors: D. E. Smith, I. D. L. Foster, D. Long and S. Shi

The widespread sheets of fine particulate sediment frequently deposited by tsunami constitute valuable evidence from which to reconstruct tsunami inundation. This is illustrated with evidence from three sites near Montrose, in eastern Scotland, U.K., where a horizon of mainly sand, laid down during the Holocene Storegga Slide palaeotsunami of circa 8000 BP is examined. The horizon is remarkably consistent in its distribution, morphology, stratigraphy, and particle size characteristics. These properties allow inferences to be made on the nature of tsunami flow onshore and run-up. It is suggested that estimates can be made of the possible depth of water involved from the characteristics of the sediment, and thus of the extent of inundation involved in the tsunami at these sites.

Tsunami deposits in the SW Montrose Basin, Scotland
The area examined in detail in this paper lies on the south-western shore of the Montrose Basin, eastern Scotland, UK. The Montrose Basin is an estuarine area at the mouth of the river South Esk, surrounded by marine terraces. The Basin is mesotidal, the present Spring tidal range  at Montrose being 4.1m (Admiralty Hydrographic Department, 1996), and recent work suggests that this is likely to have changed little over the mid-late Holocene (Shennan et al., 2000). The area has experienced glacio-isostatic uplift since the last glaciation (e.g. Cullingford and Smith,  1980; Smith and Cullingford, 1985; Smith et al., 2006), with marine terraces at several altitudes, reflecting former shorelines. The highest marine terraces surrounding the Basin were formed during and following the decay of the last (Late Devensian) ice sheet to have occupied the area. These terraces, dissected by a number of gullies, overlook raised Holocene estuarine silts to seaward. These silts form a level surface, known locally as "carseland", and for the most part probably  a relict saltmarsh. Underlying the silts (carseland) and resting upon Late Devensian deposits beneath is a layer of Holocene peat, which outcrops along the gully sides and at their heads.
Within the silts and passing landward into the peat a prominent layer of fine particulate sediment, mainly fine or medium sand, occasionally coarser but with some silt and sometimes containing  intraclasts of peat, occurs. For convenience, this layer is referred to as a sand layer in this paper.

Source (67kb, PDF)

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Blobrana


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The three Storegga Slides are considered to be amongst the largest known landslides. They occurred under water, at the edge of Norway's continental shelf (Storegga is Norwegian for the "Great Edge"), in the Norwegian Sea, 100 km north-west of the Møre coast. An area the size of Iceland slumped, causing a very large tsunami in the North Atlantic Ocean.
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Blobrana


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Around 8100 years ago, one of the largest landslides in the world occurred at Storegga, 100 kilometres north west of the Møre coast, south-west Norway. An area the size of Iceland slid into the Norwegian Sea triggering 10-meter high tsunamis.

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Blobrana


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Evidence of a massive 20 metre high Tsunami from the peat bogs in the Shetland islands.
A layer of sandy material with the remains of marine creatures are seen mixed in with large broken up pieces of peat.

Evidence of Tsumami Evidence of Tsumami1
Expand (157kb, 640 x 409)......................Expand (143kb, 640 x 409)

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Blobrana


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a massive landslide on the ocean floor off Storegga, south-west Norway, triggered a 10-meter high tsunamis.

Radiocarbon dating of sediments taken from the coastline of eastern Scotland show that a giant wave flooded Scotland about 5,800 BC. At the time, Britain was joined to mainland Europe by a land bridge.



"While there is no reason for mass panic, the possibility exists that the Storegga slide will go again, and it would be imprudent to ignore that fact"


IMAGE (69kb, 640 x 408)

The three Storegga Slides count among the largest recorded landslides. They occurred under water on the edge of Norway's continental shelf (Storegga is Norwegian for "the Great Edge") in the Norwegian Sea, 100 km north west of the Møre coast, where an area the size of Iceland slid, causing a megatsunami in the North Atlantic Ocean.



As part of the activities preparing the Ormen Lange natural gas field, the incident has been thoroughly investigated. One conclusion was that the slide was caused by material built up during the previous ice age, and that a reoccurrence would only be possible after a new ice age.

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