Lithology, strata and rates of coastal recession

Lithology

Lithology means the physical and chemical character of a rock. In general (Getting Started Guide):

• Igneous rocks (granite, basalt) are crystalline and very resistant: recession is extremely slow.
• Sedimentary rocks vary: well-cemented limestones and sandstones resist erosion; shales and clays are weak.
• Metamorphic rocks (slate, schist) are generally resistant, though foliation can create weaknesses.
• Unconsolidated material (glacial till, sand, gravel) is not cemented at all, so it is the weakest and recedes fastest.

Resistance depends on hardness, cementation, how many cracks the rock has, and how easily its minerals are attacked chemically.

Case study: the Holderness coast

Holderness in East Yorkshire is cut into soft glacial till, a mixture of clay, silt, sand, gravel, cobbles and boulders deposited by glaciers (British Geological Survey). Key figures (urbanrim.org.uk data, 2003 to 2025):

• 61.8 km of glacially deposited coast, of which 9.9 km is defended.
• Average recession 1.40 m per year for the whole coast over 23 years, and 1.65 m per year for unprotected cliff.
• Each metre of recession removes roughly 1 million cubic metres of material.
• Erosion is faster just south of the sea walls at Hornsea and Withernsea (a downdrift effect).

The BGS estimates around 1.5 m per year at Aldbrough. Compare a granite coast, where recession is negligible over a human lifetime.

Alternating strata and complex cliff profiles

Where layers of different rock alternate, differential erosion creates complex cliff profiles:

• A resistant layer over a less resistant layer: the weak layer is cut back, undercutting the strong one, which then collapses in blocks.
• Permeable rock (sandstone, chalk) over impermeable rock (clay): rainwater soaks through the permeable layer and collects at the boundary. Pore water pressure builds, the clay becomes slippery and the cliff fails by slumping or rotational sliding. Springs may emerge along the junction.

So recession rates depend not only on wave attack at the base, but also on what happens within and on top of the cliff.

Worked example

Holderness lost an average of 1.4 m per year between 2003 and 2025. Estimate the total recession over those 23 years.

1. Total = rate x time = 1.4 x 23
2. = 32.2 m

Answer: About 32.2 m of retreat (an average; actual loss varies from place to place and year to year).

Check yourself

1. Holderness has 9.9 km of defences along 61.8 km of coast. What percentage of the coast is defended? Give your answer to 1 decimal place.
   Show answer

   16.0 %. 9.9 / 61.8 x 100 = 16.0%.

2. Unprotected Holderness cliff retreats about 1.65 m per year. How far would it retreat in 20 years at that rate?
   Show answer

   33 m. 1.65 x 20 = 33 m.

3. Which material usually has the fastest rate of coastal recession?
   • Unconsolidated glacial till
   • Granite
   • Basalt
   • Slate
   Show answer

   Unconsolidated glacial till. Till is uncemented, so waves remove it easily.

4. A cliff has permeable sandstone resting on impermeable clay. What is the most likely form of failure?
   • Freeze-thaw shattering of the clay only
   • Formation of a stack
   • Longshore drift
   • Rotational slumping as water collects at the clay boundary
   Show answer

   Rotational slumping as water collects at the clay boundary. Water builds pore pressure at the junction and the cliff slumps.

5. Differential erosion means
   • erosion only by rivers
   • rocks of different resistance eroding at different rates
   • deposition of different sediment sizes
   • erosion at the same rate everywhere
   Show answer

   rocks of different resistance eroding at different rates. Weaker layers retreat faster, leaving resistant ones standing out.

6. Each metre of Holderness recession removes about 1 million cubic metres. Using the whole-coast mean of 1.4 m per year, about how many million cubic metres are lost each year?
   Show answer

   1.4 million m3. 1.4 m x 1 million m3 per m = 1.4 million m3.

7. Explain why a granite coast recedes much more slowly than a till coast.
   Show answer

   Granite is a crystalline igneous rock that is hard and has few weaknesses, so waves erode it very slowly, whereas till is unconsolidated and easily removed.. Contrast the two materials and link to rate.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Geography specification, Issue 3 (September 2025)
• Pearson IAL Geography Getting Started Guide
• British Geological Survey: Coastal erosion (Aldbrough, Holderness)
• Holderness coast data (urbanrim.org.uk): erosion 2003 to 2025, geology and defences

Last updated 8 November 2026. Spotted a mistake? Tell us.