4 November 2012, GSA Annual Meeting, Charlotte, NC Can improved understanding of frost cracking help to anticipate focal zones for rockfall from degrading permafrost? Stephan Gruber, Lucas Girard, David Amitrano, Jan Beutel, Samuel Weber Photo: B. Jelk 4 November 2012, GSA Annual Meeting, Charlotte, NC Motivation: Anticipating where to expect surprise Permafrost maps constrain the area of potential surprise (a bit). Ideally, we want to constrain locations even further. But how? Empiricism with rock falls is difficult: low frequency, strong heterogeneity, non-stationarity Gruber 2012 Boeckli et al. 2012 4 November 2012, GSA Annual Meeting, Charlotte, NC Conceptual model of (slow) rock-fall preconditioning in permafrost Cleft ice can be: active agent passive infill Gruber & Haeberli 2007 4 November 2012, GSA Annual Meeting, Charlotte, NC The formation of an ice-rich transient layer in compact rock is plausible Pollard & French (1980) Murton et al. (2001) Shur et al. (2005) Volumetric ice content [%] Depth [m] 4 November 2012, GSA Annual Meeting, Charlotte, NC Thermal, hydrologic and erosional conditions in walls and ridges Temperature induces favorable gradients in hydraulic permeability. Frequent and ample supply of moisture on sunlit slope. Surface erosion limits the age of the transient layer. In compact rock walls, surface 10 Be ages of 38ka have been measured (Boehlert et al. 2008). Noetzli et al. 2007 4 November 2012, GSA Annual Meeting, Charlotte, NC Strategy and methodology Hypotheses: An ice-rich layer can form by segregation, even in compact rock. Understanding its formation can be up-scaled with models to pin-point focus areas. Assumptions: AE are useful to detect small increments of damage. Near-surface is data-rich and less expensive. Current aim: Understand mechanisms and their drivers. Demonstrate robust scaling from lab/theory to field. Future aim: Numerical exploration of behavior and scaling. Where is significant fracturing plausible? Deeper measurements could test transient layer in focal area. 4 November 2012, GSA Annual Meeting, Charlotte, NC Acoustic emission monitoring: Instrumentation and field set-up Depth 10cm 50cm 100cm AE sensors Liquid H 2 O sensor Temperature sensor Girard et al Weber et al cm 4 November 2012, GSA Annual Meeting, Charlotte, NC Installation overview spur, dryer site gully, wetter site 4 November 2012, GSA Annual Meeting, Charlotte, NC Installation and webcam image 4 November 2012, GSA Annual Meeting, Charlotte, NC Measured time series (gully, wet site) black: 10 cm red: 50 cm Lucas Girard et al., ongoing Thawed energy and event rates are only a few percent (0.057) of the frozen ones. During freezing, energy rates at the wet site are about 10 times larger than at the dry one. 4 November 2012, GSA Annual Meeting, Charlotte, NC Freezing characteristics and re-wetting after drilling wet site, Apr-Oct 2012 wet site, Jan-Mar 2012 dry site, Apr-Oct 2012 dry site, Jan-Mar 2012 Lucas Girard et al., ongoing 4 November 2012, GSA Annual Meeting, Charlotte, NC Influence of freezing (at 50 cm) spur, dryer site gully, wetter site Lucas Girard et al., ongoing 4 November 2012, GSA Annual Meeting, Charlotte, NC Freezing vs thermal stress Lucas Girard et al., ongoing warming cooling warming cooling 4 November 2012, GSA Annual Meeting, Charlotte, NC Power-law scaling appears independent of freezing Lucas Girard et al., ongoing 4 November 2012, GSA Annual Meeting, Charlotte, NC Thank you. Questions? Find full references, paper PDFs and links in the PDF of this talk. 4 November 2012, GSA Annual Meeting, Charlotte, NC Links and references Amitrano, D., Gruber, S., & Girard, L. (2012): Evidence of frost-cracking inferred from acoustic emissions in an high-alpine rock- wall, Earth and Planetary Science Letters, 341344, 8693, doi: /j.epsl PDF:Boeckli, L., Brenning, A., Gruber, S. & Noetzli J. (2012): Permafrost distribution in the European Alps: calculation and evaluation of an index map and summary statistics, The Cryosphere, 6, 807820, doi: /tc PDF:Bhlert, R., Gruber, S., Egli, M., Maisch, M., Brandov, D., Ivy-Ochs, S., Kubik, P.W., Deline, P. & Haeberli, W. (2008): Comparison of exposure ages and spectral properties of rock surfaces in steep, high Alpine rock walls a field study at Aiguille du Midi, France, Proceedings of the 9th International Conference on Permafrost 2008, Fairbanks, Alaska, USA, 143148. PDF:Girard, L., Beutel, J., Gruber, S., Hunziker, J., Lim, R. & Weber, S. (accepted): A custom acoustic emission monitoring system for harsh environments: application to freezing-induced damage in alpine rock-walls, Geoscientific Instrumentation, Methods and Data Systems. PDF:Gruber, S. & Haeberli, W. (2007): Permafrost in steep bedrock slopes and its temperature-related destabilization following climate change, Journal of Geophysical Research, 112, F02S18, doi: /2006JF PDF:Gruber, S. (2012): Derivation and analysis of a high-resolution estimate of global permafrost zonation, The Cryosphere, 6, 221 233, doi: /tc PDF:Online data:Noetzli, J., Gruber, S., Kohl, T., Salzmann, N. & Haeberli, W. (2007): Three-dimensional distribution and evolution of permafrost temperatures in idealized high-mountain topography, Journal of Geophysical Research, 112, F02S13, doi: /2006JF PDF: /2006JF000545www.geo.uzh.ch/~stgruber/pubs/noetzli_2007-JGR.pdf Weber S., Gruber S., Girard L. & Beutel, J. (2012): Design of a measurement assembly to study in-situ rock damage driven by freezing, Proceedings of the 10th International Conference on Permafrost, 2529 June 2012, Salekhard, Russia, 437442. PDF:Further information and data available at:and data.permasense.ch.www.permasense.chdata.permasense.ch