Integrating Monitoring Techniques for a Buried Sinkhole in an Urban Environment

Ripon is a historic city and market town in North York - shire. It is unique in being the only city in the UK to define planning zones based on the potential for bedrock dissolu - tion. The underlying geology comprises marls, limestone and gypsum of the Permian Edlington, Brotherton and Roxby formations, capped by glacial deposits (till). It is the rapid rate of dissolution of the gypsum (hydrated calcium sulphate) that enables the karst to evolve on human time scales. Following the collapse that formed a sinkhole in the rear garden of a property in Magdalens Road, Ripon, UK in November 2016 the British Geological Survey, funded by a Natural Environment Research Council grant, initiated a programme of monitoring of a nearby depression. This feature is forming in a recreation area and is one that local residents reported to have grown in dimensions. The density of development precludes the use of satellite-based monitoring systems. Instead, we have inte - grated ground-based LiDAR imaging with geophysical techniques (micro-gravity and passive seismic). Moni - toring has revealed that this depression lies over a pal-aeosinkhole that is in the order of 10 m in diameter and extends to a depth of a similar order of magnitude. The monitoring has been continued in the context of PhD research (University of Sheffield) that is more broadly focused on understanding sinkhole triggering processes. The developing sinkhole is on the eastern side of Ripon close to the southerly flowing River Ure, where upwell - ing confined groundwater contributes to the river base flow. In this context the hypotheses that growth can be correlated with rainfall or river discharge can be tested.