The aim of this study is to investigate the relation between the critical failure stresses for rupture and pillar instabilities observed in tuffs in Cappadocia region and stresses triggering the early crack propagation stages such as crack initiation, systematic cracking and crack coalescence thresholds determined from Brazilian and uniaxial compression tests on rock samples obtained from these instabilities. These failures in the region have been occurring as a result of strength reduction of rocks through time, and long-term strengths of these rocks are achieved by own weight of the rock mass. In this study, these failures were evaluated in order to estimate long-term failure strength of rocks by classical short-term laboratory tests. For this purpose, some cases on rock rupture phenomenon and a pillar failure case were picked from different parts of the region. During the selection of these instabilities, the ones with relatively regular geometries were preferred. Rock block samples were collected from each case, and uniaxial compressive and indirect tensile (Brazilian) tests were carried out on dry and saturated specimens. In these tests, axial deformations and acoustic emission (AE) activity were also recorded in order to identify thresholds of the crack propagation and deformation stages of rock samples. the simplified back-analys is of each case was conducted, and the tensile stresses on rupture surfaces and uniaxial compressive stress on pillar were calculated. Then, stress levels at the thresholds of crack propagation and deformation stages determined by laboratory tests and stress levels determined by back-analyses were compared. Finally, it is concluded that crack initiation and/or systematic cracking thresholds may be a good indicator to determine lower bound of the in-situ strength of these tuffs and can be used as an estimator of their long-term strengths. (C) 2009 Elsevier Ltd. All rights reserved.