SUMMARY

Gypsum in the cliff on the west bank of the River Ure at Ripon Parks is being dissolved by the river. The solution rate has been determined from the solution of a large fallen block in the river and is close to laboratory experimental values. In the centre of the river and around the gypsum block flow rates of 1 m/s have been measured. Laboratory based experiments suggest that such rates would produce undercutting of massive gypsum at about 1.7 m/year. However, flow rates adjacent to the cliff are substantially reduced and much slower rates of undercutting, around 0.10 to 0.18 m/year, are predicted. Observed minimum rates of undercutting are close to these values. The massive gypsum at the southern end of the cliff appears to have been undercut up to 5 m in 50 to 60 years, i.e. between 0.10 and 0.08 m/year, and the northern part of the cliff has been undercut a similar distance in around 100 years.