The Isle of Wedmore relay ramp: how fault evolution created King Alfred's historic landmark

The Isle of Wedmore covers an area of ~ 19 km2, rises up to ~ 65 m above the surrounding lowlands of the Somerset Levels, and was an island until the Middle Ages. The topography is interpreted as having been formed by a relay ramp between two right-stepping faults (the Weare Fault to the west and the Mudgley Fault to the east) which have tens of metres of downthrow to the south, and which are probably normal faults. The relay ramp has a dip of about 3° to the SW and is breached by the NW-striking Wedmore Fault, which has up to ~ 23 m downthrow to the NE. Several NE-trending faults occur in the relay ramp, which are interpreted as having formed when the relay ramp became a contractional step when the Weare and Mudgley faults underwent sinistral reactivation, or as N–S contraction occurred during the Cenozoic. Analogues for this behaviour are presented from the Liassic rocks on the coast between Lilstock and East Quantoxhead.