User talk:Ungtss/Rapid bending granite

In the report by Hidebumi Itō and Naoiti Kumagai, "On a New Creep Experiment of Large Granite Beam Started in 1980" and Kumagai’s “Two Findings in Long-Term On-Going Laboratory Experiments on Creep of Granite Beams by Bending” the creep of a granite bar 2150 mm long under small (2 MPa maximum pressure) loads show a deflection rate of 0.005 mm/year for 30 years and an associated viscosity (μ) of 5.3X10 19 Pa-s for a sample kept near 23.9C. At that rate, it would take ~100000 years to deform to a 1m radius. If we take granite viscosity at higher temperature we get μ =10 12 at 1075.7 – 1124.8 K. Using the earth conditions at ~1.7km depth  we have a differential stress of 40 MPa and an ambient temperature of 40C (317.05 K). Assuming an Arrhenius equation for the thermal dependency of granite viscosity these values and temperatures give μ = 9.2X10 18 -1.4X10 19 at 317.05K. Since viscosity is defined as stress/(strain rate), the viscous deflection rate is linear in both stress and viscosity, giving us a time of ~1000-1500 years to get the same 1m radius. This amount of time appears to be short enough to fit into anybody’s geological time frame.