CASE STUDY - Saltburn to Flamborough Head (high-energy coastal environment)

Question 1

Geology

Answer 1

• Adjacent North York Moors rise up to 400m above sea level and comprise mainly sandstones, shales and limestones formed during the Jurassic periods as well as some carboniferous rocks
• Flamborough Head, at the southern end of this stretch of coastline, is a large chalk headland, its spectacular cliffs are topped with till (a superficial deposit left behind by glaciers during the Devensian glacial period
• Differences in rock resistance are responsible for the varied coastal scenery, notably the high cliffs and the bay and headland sequence

Question 2

Energy

Answer 2

• Dominant waves affecting this coastline are from the north and north-west, with a fetch of over 1500km
• The most exposed parts of the coast are those that are north-facing, such as the area nearest to Saltburn and so these receive the highest inputs of wave energy
• Rates of erosion vary, partly due to these differences in wave energy inputs, but also due to variations in the resistance of the difference geologies
• Areas of relatively weak shale and clay experience erosion rates of 0.8m per year on average, while the more resistant sandstones and limestones only erode at rates of less than 0.1m per year
• Monitoring of wave height using floating buoys in Whitby Bay during 2010-11 revealed that wave height often exceeded 4m, even during summer months
• The high energy inputs are also responsible for the significant longshore drift from north to south along the coastline, in places this sediment movement is interrupted by headlands and sand and shingle then accumulate to form beaches in the bay, such as Filey and Clayton

Question 3

Sediment sources

Answer 3

• Coastline between Saltburn and Flamborough is sub-cell 1d of the major sediment cell 1, which extends south from St Abbas in southern Scotland to Flamborough
• Some of the sediment in sub-cell 1d has come from the nearshore area, driven on-shore as sea levels rose at the end of the last glacial period
• Sediment is also supplied by cliff erosion, including sandstone and chalk from the resistant rock outcrops and the boulder clay deposits which yield significant amounts of gravel
• The only large river, the Esk, enters the North Sea at Whitby, this supplies limited amounts of sediment due to the construction of weirs and reinforced banks along its course
• Beach surveys have found that there had been a net increase in beach sediment of 9245 m^3 between 2008 and 2011 at Saltburn
• Zones of beach erosion and accretion were observed within Filey Bay, which reflect the influence of winter storm systems with erosion at the back of the beach being particularly significant in the winter of 2010-11

Question 4

Cliffs

Answer 4

• The sedimentary rocks of this coastline are horizontally bedded, and as a result the cliff profiles tend to have a vertical face
• Most cliffs are overlain by a layer of weak glacial till, which has a much lower angle
• Cliffs at Flamborough are made of chalk, which is physically very strong with tightly bonded mineral particles
• The vertical cliffs are typically 20-30m high, with the overlying till lowered by mass movement processes to an angle of about 40 degrees
• Further north, between Robin Hood’s Bay and Saltburn, the cliffs are much higher, but often with a stepped profile, reflecting the more varied geology
• The steeper slope segments are formed in the more resistant sandstones and limestones, with gentler slopes corresponding to the weaker clays and shales, again lowered by mass movement processes

Question 5

Shore platforms

Answer 5

• High energy waves and active erosion mean that cliffs are retreating along this coastline, leaving behind rocky shore platforms
• Good example can be seen at Robin Hood’s Bay, eroded into Lower Lias shales, the platform slopes at a typical angle of 1 degree, although ramped sections are as steep as 15 degrees
• The platform has a maximum width of about 500m, but extends much further into the off-shore zone
• Based on current rates of erosion and retreat, it is quite possible that platform such as these could have been formed within the last 6000 years, during times of predominantly stable sea level
• However, some experts suggest that they are relict features, formed during earlier inter-glacial periods when sea levels were similar to those of today

Question 6

Headlands and bays

Answer 6

• Variation in rock type along the coastline has led to the formation of a seres of bays and headlands as part of a discordant platform
• Robin Hood’s Bay has been eroded into relatively weak shales with more resistant bands of sandstone either side forming the headlands of Ravenscar to the south and Ness point to the north
• Further south, Filey Bay has developed in weak Kimmeridge Clay and is flanked by more resistant limestone and chalk
• The prominent headland at Flamborough is formed of chalk, with deep bays either side formed from clay

Question 7

Landforms on headlands

Answer 7

• Due to wave refraction, wave energy is concentrated on resistant headlands that project into the North Sea
• Weaknesses, such as large joints or faults are then exploited by the erosive action of the waves, enlarging them to form caves and arches
• These features are clearly visible in Selwick’s Bay at Flamborough Head, where a master joint in the chalk has been enlarged
• Green Stacks Pinnacle is an example of a stack, isolated at the end of a headland, following the collapse of an arch roof
• Ovr 50 geos have formed along this coastline, with most of them aligned to the NE or NNE, facing the dominant wind direction
• Blowholes have developed where vertical master joints in the chalk have been enlarged, subsequently chalk and boulder clay have collapsed into the underlying sea caves, leaving funnel-shaped depressions on the cliff tops
• On the north side of Selwick’s Bay, several blowholes appear to have merged and the intervening chalk has collapsed to produce a complex inlet

Question 8

Beaches

Answer 8

• There are very few well-developed beaches along this stretch of coastline
• Best examples found in the sheltered, low-energy environments such as Runswick Bay and Filey Bay
• Deposits of sand and shingle accumulate slowly owing to the low input of sediment from rivers and the slow rates of erosion of the resistant rocks
• High-energy waves also remove sediment before it can accumulate
• Although longshore drift is considerable, the coastline lacks spits and other drift-aligned features, this is due partly to the high tidal range of around 4m and the lack of estuarine environments that would provide sediment sinks