The Earth Story

Original caption:

The Quiraing Slide

These large blocks of exposed sedimentary rock are just a small part of what is known as the Quiraing Slide complex, found on the Isle of Skye. The slide is enormous, one of the largest known in Europe. Altogether, an area 45 kilometers wide of rock that was once part of an elevated plateau has broken away and slide downhill at least 6.5 kilometers.

These big blocks of sediment are Jurassic in age, formed in basins off to the side of the major mountain ranges created when Pangaea was assembled. During the Tertiary about 50 or 60 million years ago, this part of Scotland pulled away from Greenland, forming the North Atlantic Ocean. This process fractured the rocks, formed faults and joints, and also created outpourings of lava that covered the sediments.

The combined weight of the lava and sedimentary rocks was more than weak layers in the sequence could bear. Old faults and weak sedimentary layers buried in the sequence failed and large chunks of the plateau began breaking loose. They have moved downhill in a variety of ways – some large blocks rotated, some failed as mudflows, some fell over, some moved slowly, some moved catastrophically.

A brief search of the scientific literature on this area does not tell me when these rocks began moving, but it does tell me that the blocks are expected to continue moving and may eventually threaten infrastructure downslope.

-JBB

Image credit: https://flic.kr/p/WxfAxY

References: http://bit.ly/2wj2tKt http://bit.ly/2tWTRZd

The Quiraing The landslide visible in the photo is still gently slipping, and is the largest one in Britain. The road winding through the marvellous glacier sculpted landscape of the Isle of Skye at the bottom of the slip needs consequent repairs every year. Skye is located off the Scottish mainland, and Trotternish Ridge is the source of the slide and hosts a popular walking trail. Other landslips are visible in the background, as the forces of erosion repeatedly peel layers off the cliff (known as an escarpment) that then slump down the slope. The ridge probably represents a weak line in the rocks, since its formation is entirely due to this phenomenon.  Five stages of movement have been traced by geomorphologists (those who study the surface shape of the Earth and how it was formed). The rocks are fossil rich Jurassic marine sediments, composed of clays, shales and sandstones, overlain by tertiary basaltic lava flows some 300 metres thick, whose weight peeled the sediments off the cliff. The name comes from the old Norse for round fold, and reputedly sheep were hidden there from raiding Vikings.  Alot of 'the Isles' (as my favourite historian called them, as he navigated a careful and sensitive route through the maze of identities, past and modern, that are present in Yneis Pryrdein) best geology lies north of the Scottish border, and I'm personally grateful I won't need to bring my passport in order to visit it.  Loz Image credit: Dougie Cunningham http://www.rgs.org/OurWork/Schools/Teaching+resources/Key+Stage+3+resources/Adventure+landscapes/A+walk+around+the+Quiraing.htm http://www.isleofskye.com/skye-guide/top-ten-skye-walks/the-quiraing http://www.theskyeguide.com/walking-mainmenu-32/13-moderate-walks/128-quiraing