Applied Geography (1981), 1, 297-304 c 1981 Butterworths 29-l Short Communication The persistence of oil pollution on a rocky shore D. N. Mottershead Edge Hill College of Higher Education, Ormskirk, England Abstract Spots of oil thrown up on to a coastal rock platform just above high water mark protect the rock beneath from weathering. Differential weathering subsequently leads to the emergence of oil-capped pedestals. Measurement of the rate of bedrock lowering of the surrounding surface by micro-erosion meter (MEM) provides a method of estimating the age of the pedestals and consequently the duration of oil persistence on the shore. The maximum duration of oil is estimated at l7- I8 years. Introduction The ever-increasing prevalence of spills of oil in coastal waters causing onshore pollution has attracted much attention in recent years. Interest to date, however, has tended to focus on the economic and ecological consequences. The present paper reports on unusual and unexpected geomorphological consequences. It was apparent upon close inspection that small spots and patches of oil on a rock platform immediately above high water mark (HWM) were protecting the underlying rock from weathering and erosion, thereby causing differential erosion. Thus the oil has acted as a kind of protective cap, allowing small pedestals to develop as the surrounding rock surface continued to be lowered. This in turn suggested that the rate of lowering may be unusually rapid, and therefore worthy of, and susceptible to, direct measurement. A further corollary of this inference is that the rate of lowering, once determined, can be used to provide an estimate of the age of the pedestals, and hence the duration of the oil pollution on the shore. The field area The features described in this paper are located on the coast of South Devon, some 4km west of Start Point, and close to the village of East Prawle (Fig. 1). The coastline is rocky in nature, and is composed of the greenschist facies of the Start schist complex (Ussher 1904; Tilley 1923). These rocks are mechanically strong in the unweathered state, and strongly jointed, and form a craggy and irregular shore zone. The South Devon coast can be described as a macrotidal storm wave environment (Davies 1964). Tides are semi-diurnal with a range at high springs at nearby Dartmouth of 5.2m. The exposed nature of the coastline, allied to the fact that waves break upon the rocky shore, means that spray is frequently thrown up well above HWM. Indeed, with onshore winds and stormy conditions there may be a continuous mist of fine spray hanging over the shore.