Tidal stress

Tidal breakup is not, however, the major source of fragmentation of comets. Most fragmentation occurs somewhat mysteriously far from massive bodies in the absence of tidal stress. Many comets including S4 LINEAR, Hale-Bopp, Wilson, Kohoutek, West, and Ikeya-Seki have been seen to fragment far from the Sun and Jupiter. Remarkable insight into the disintegration of comets has come from the study of the Kreutz family of sungrazing comets, a family of comets that pass within a few solar radii of the Sun. 

The tides also have important effects on the dynamics (both rotation and orbit) of Europa. Because the orbit is eccentric, tidal torques tend to drive spin to a state that is slightly faster than synchronous (Greenberg and Weidenschilling 1984). This effect in turn can increase the tidal stress on the surface substantially, although it acts on a much longer timescale ( -MO5 years) than the 3 1/2 day orbital period. The tides also effect the long-term evolution of the orbits of the satellites, so that the Laplace resonance itself probably changes over MO7 years or more. 

Tidal theory applied to observations of tectonic and thermal features suggests that the ice is significantly thinner, so that the ocean can connect with the surface through cracks and melt sites. Tidal stress can probably open cracks no deeper than a few km, so we infer that the ice is probably less than 10 km thick. 

Both tectonic cracks and thermally produced Chaotic terrain are caused by tides, and both involve linkage of the underlying ocean to the surface. The darkening associated with each of these formation processes probably involves substances from the ocean, which makes the features visible even at the low resolution of global images like Figure 5. The cracks are caused by tidal stress and the chaos is probably caused by melt-through of patches of crust by tidal heat. 

The mechanism by which tides create the cycloidal crack patterns was discovered by B.R. Tufts and G.V. Hoppa (Hoppa et al. 1999c). Due to the orbital eccentricity, which is pumped and maintained by the Laplace resonance, the tidal stress on Europas ice crust changes periodically with each orbit. We call this variation the diurnal tide, because the 85 hr orbital period is approximately the length of a Europan day, and is comparable to the length of a day on Earth. 

Strike-slip displacement, in which one crustal plate shears past another, is relatively rare in the solar system except in a few places. On Earth, with its global tectonics, strike-slip between plates is well known. The San Andreas fault in California is a famous example. Similar strike-slip is ubiquitous on Europa. Faults there include some longer than the San Andreas, with Strike-slip displacement of tens of km. Strike-slip displacement on Europa is probably driven by diurnal tides, and thus by the Laplace resonance. Over the course of a day, the tidal stress follows a sequence that can open a crack, shear it, then close it. Then, stress that would reverse the shear is resisted while the crack is closed. This process repeats on a daily basis. In this process, which is analogous to walking, one plate of crust can shear past another, with Strike-slip displacement visible along the boundary. This process has been described in detail by Hoppa et al. (1999b). 

Distribution of strike-slip faults on Europa. JGR, pages 22617-22628. Hoppa, G., Tufts, B. R., Greenberg, R., and Geissler, P. (1999b). Strike-Slip Faults on Europa Global Shear Patterns Driven by Tidal Stress. Icarus, 141 287-298. 

In the tidal zone and the spray zone (known as the splash zone), cathodic protection is generally not very effective. Here thick coatings or sheathing with corrosion-resistance materials (e.g., based on NiCu) are necessary to prevent corrosion attack [4]. The coatings are severely mechanically stressed and must be so formed that repair is possible even under spray conditions. Their stability against cathodic polarization (see Section 17.2), marine growths, UV rays and seawater must be ensured [4,5]. 

Quijano-Guerta C, Kirk GJD. 2002. Tolerauce of rice germplasm to saliuity aud other soil chemical stresses in tidal wetlands. Field Crops Research 76 111-121. 

The presence of these compounds in the Delaware River may have some health implications. If the discharge site at river mile 104 is correct, then these compounds would enter the river only four miles downstream from the inlet for Philadelphia s drinking water. Tidal action is sufficient to carry these chemicals upstream to the inlet and, in fact, the volatile ethers, bls-(2-chloroethyl) ether, and l,2-bis(2-chloroethoxy) ethane, have been found in the drinking water supply (29). Health effects, notably the carcinogenic activity, of these compounds are not known. It should be stressed that the higher molecular weight compounds (no. 65-70) have not yet been detected in the drinking water nor have their health effects been evaluated. 

In a related experiments, shallow and deep water forms were compared327. In deep water specimens increments had a uniform thickness, without sharp boundaries and no apparent seasonal or tidal indications. In summary microgrowth patterns reflect environmental changes of many sorts. The ultimate reason behind this phenomenon can be explained on physiological grounds as a result of the utilisation of calcium in energy transfer and muscle activities. Namely at times of stress these activities have higher priorities than calcification. 

Hofmann, G.E., and G.N. Somero (1996a). Protein ubiquitination and stress protein synthesis in Mytilus trossulus occurs during recovery from tidal emersion. Mol. Mar. Biol. Biotech. 5 175-184. 

The patterns of successional dynamics of mangrove forests are related to the environmental tolerances of the species, and often result in distinct community zone types within this ecosystem. Usually the succession culminates in a mature forest of mangrove species. However, in some cases succession in the mangrove ecosystem can sufficiently reduce the influence of tidal waters to allow relatively fresh-water conditions to develop. Under these circumstances succession can result in the development of a relatively species-rich forest that is lacking in mangrove species, because these are not very competitive under the less stressful conditions of fresh water. 

Lindzen, R.S., Turbulence and stress owing to gravity wave and tidal breakdown. J Geophys Res 86, 9707, 1981. 

This tidal tectonic process was described by Greenberg et al. (1998). A key point is that the magnitude of the tidal tensile stress is probably not adequate to open cracks to a depth greater than a few km, because the overburden compression would be too great at depth. Therefore for this ridge-building process to work, the ice must be fairly thin. 

Currents in the Sound are due to the tidal stream, to the estuarine circulation, and to wind stress acting on the water surface. Systematic surveys of the currents in the Sound have been made from time to time by the U.S. National Ocean Survey. Current meters have been placed in grid-pattern arrays for time intervals sufficiently long to reveal the principal tidal constituents of the current. Data obtained this way were used by G. A. Riley (1952, 1956) to describe the estuarine circulation of the Sound. The utility of these meter records in the study of sediment transport is limited because the observations were all made during the... 

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