Shocked rocks

P. Lambert, Rcflcclivily applied to jicak picssiuc esliinalcs iii. silicates ol shocked rocks. J. Geophys. Res. 86, pp. 6187-6204 (11)81). 

Q-Quartz, which has a trigonal crystal structure, undergoes a rapid, reversible transition to hexagonal /J-quartz at 573 °C and then slowly changes to hexagonal /3-tridymite at about 870 °C tridymite in turn goes over slowly to cubic /3-cristobalite at 1470 °C, and this melts at 1713 °C. The reversion of cristobalite and tridymite to quartz is slow, so that these forms can exist at room temperature (as a-modifications). In addition, dense modifications with six-coordinate Si are found in shocked rocks associated with meteorite impact craters coesite forms only above 450 °C and 3.8 GPa, and stishovite requires over 1200 °C and 13 GPa. Survival of those metastable polymorphs on the geological timescale is evidence of an extremely slow recrystallization rate. 

Ground or crushed rock coverings, about 80-150 mm thick, are useful to slow the evaporation of soil moisture and hence retain the moisture of the topsoil layers. It will also diminish the intensity of shock currents due to higher contact resistance between the feet and the soil. Typical values may vary from 1000 to 5000 Qm. 

Grady, D.E. (1977), Processes Occurring on Shock Wave Compression of Rocks and Minerals, in High Pressure Research Applications in Geophysics (edited by Manghnani M.H. and S. Akimoto), Academic Press, New York, pp. 389-438. 

Stdffler, D. (1972), Deformation and Transformation of Rock-Forming Minerals by Natural and Experimental Shock Processes, I, Fortschr. Miner. 49, 50-113. 

T.J. Ahrens and G.E. Duvall, Stress Relaxation Behind Elastic Shock Waves in Rocks, J. Geophys. Res. 71, 4349-4360 (1966). 

Ivanov, A.G. and V.N. Mineev (1980), Explos. Combust. Shock Waves 15, 617-638. Jaeger, J.C. and N.G.W. Cook (1969), Fundamentals of Rock Mechanics, Chapman and Hall, New York. 

One of the major effects of acidic deposition is felt by aquatic ecosystems in mountainous terrain, where considerable precipitation occurs due to orographic lifting. The maximum effect is felt where there is little buffering of the acid by soil or rock structures and where steep lakeshore slopes allow little time for precipitation to remain on the ground surface before entering the lake. Maximum fish kills occur in the early spring due to the "acid shock" of the first meltwater, which releases the pollution accumulated in the winter snowpack. This first melt may be 5-10 times more acidic than rainfall. 

The drill string is defined here as a drill pipe with tool joints and drill collars. The drill stem consists of the drill string and other components of the drilling assembly that includes the kelly, subs, stabilizers, reamers as well as shock absorbers, and junk baskets or drilling jars used in certain drilling conditions. The drill stem (1) transmits power by rotary motion from the surface to a rock bit, (2) conveys drilling fluid to the rock bit, (3) produces the weight on bit for efficient rock destruction by the bit, and (4) provides control of borehole direction. 

Axial vibrations usually occur in vertical boreholes and hard rock drilling with tricone bits. They can cause top drive shaking, Kelly bouncing, and induce downhole shocks. Axial vibrations can be minimized by changing the WOB and rotary RPM after rotation comes to a complete stop. Change the bit type may also help. 

Drilling surface data such as weight-on-bit and torque were difficult to interpret because they were loosely related to downhole values. MWD for the first time in the history of drilling gives values of parameters measured at the bit or close by. Rock strength, bit wear, drag and friction can be calculated in real time. Shocks, temperature and pressure can also be measured. 

The process of detonation in an explosive, the blasting effects of such an explosive in coal or rock, and the destructive effects of military high explosives all depend on the operation of shock waves. It is, therefore, intended to give here an elementary account of shock waves in inert media and in explosives before discussing individual high explosives. 

The maximum potential power of an explosive can be calculated, or it can be measured by techniques such as those developed by Cook. A typical method consists of firing the explosive under water and measuring the energy liberated in the various forms, such as shock wave in the water, the work of expansion of the gas bubble, etc. These figures have limited practical value as the methods of application of explosives are of low and variable efficiency. A more practical measurement of strength can be obtained by the measurement of cratering efficiency. This, again, demands considerable expense and also requires the availability of uniform rock. 

After the shock wave has passed through the rock the borehole still contains hot gases at high pressure. As there are now fissures in the rock, however, the strength is reduced to a negligible amount and the gases can expand and throw the broken rock away from the solid mass. 

E. L. Shock (1990) provides a different interpretation of these results he criticizes that the redox state of the reaction mixture was not checked in the Miller/Bada experiments. Shock also states that simple thermodynamic calculations show that the Miller/Bada theory does not stand up. To use terms like instability and decomposition is not correct when chemical compounds (here amino acids) are present in aqueous solution under extreme conditions and are aiming at a metastable equilibrium. Shock considers that oxidized and metastable carbon and nitrogen compounds are of greater importance in hydrothermal systems than are reduced compounds. In the interior of the Earth, CO2 and N2 are in stable redox equilibrium with substances such as amino acids and carboxylic acids, while reduced compounds such as CH4 and NH3 are not. The explanation lies in the oxidation state of the lithosphere. Shock considers the two mineral systems FMQ and PPM discussed above as particularly important for the system seawater/basalt rock. The FMQ system acts as a buffer in the oceanic crust. At depths of around 1.3 km, the PPM system probably becomes active, i.e., N2 and CO2 are the dominant species in stable equilibrium conditions at temperatures above 548 K. When the temperature of hydrothermal solutions falls (below about 548 K), they probably pass through a stability field in which CH4 and NII3 predominate. If kinetic factors block the achievement of equilibrium, metastable compounds such as alkanes, carboxylic acids, alkyl benzenes and amino acids are formed between 423 and 293 K. 

However, cavitation may result in an even more serious condition than vapor lock. When the pressure at any point within the pump drops below the vapor pressure of the liquid, vapor bubbles will form at that point (this generally occurs on or near the impeller). These bubbles will then be transported to another region in the fluid where the pressure is greater than the vapor pressure, at which point they will collapse. This formation and collapse of bubbles occurs very rapidly and can create local shock waves, which can cause erosion and serious damage to the impeller or pump. (It is often obvious when a pump is cavitating, because it may sound as though there are rocks in the pump )... 

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