Bridges, MC 2013, 'An extensional mechanism of instability and failure in the walls of open pit mines', in PM Dight (ed.), Slope Stability 2013: Proceedings of the 2013 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, pp. 137-150, https://doi.org/10.36487/ACG_rep/1308_03_Bridges (https://papers.acg.uwa.edu.au/p/1308_03_Bridges/) Abstract: Evidence from studies of instability and failures in the walls of open pit mines and cuttings indicates a predominance of an extensional mechanism, comprising toppling, ravelling and creep-subsidence. This is interpreted to arise from relief and dilation when a pit wall is excavated, removing overburden and lateral confinement of the wall. Evidence does not support sliding and shear or shallow toppling mechanisms of instability or failure.