The Lias Group encompasses some of the most important geological
formations in Britain. The Lias has been involved in a number of major engineering
projects, explored for industrial use and investigated in scientific research
over the last two centuries.
The Lias Group consists mainly of clays, mudstones and limestones
of Late Triassic and Early Jurassic age, deposited between 180
and 205 million years ago.
The outcrop of the Lias extends in a continuous
band from the south coast of Dorset to Yorkshire, with some outlying areas in
Somerset and South Wales.
Significant outcrops are found in the high
sea-cliffs on the coasts of Dorset, South Wales, and Yorkshire.
Geological Hazards and Geotechnical Problems
Much of the Lias has high sulphate content and is responsible for high levels of thaumasite concrete attack.
Lias clays contain the clay mineral smectite, and are hence prone to swelling and shrinking. The smectite content of the Lias Group is variable, and whilst the Lias overall has a ‘medium’ volume change potential rating, some formations contain smectite-rich layers which have a ‘high’ rating.
The Lias Group rocks are recorded as having the highest incidence of landsliding in the UK. The Upper Lias (Whitby Mudstone Formation) having as many as 42 landslides per 100 km² of outcrop.