Bedrock Topography

A radar-echo profile of the edge of the ice sheet in the Allan Hills in Fig. 17.22 also reveals the presence of a subglacial ridge. The ice flowing across this ridge 

Bedrock ridge composed of sandstone and dole rite 

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The link between drought and increased S04 flux is, at least in part, through the S redox cycle, Lower water tables in the wetlands and riparian areas, and even in sub-surface pools that result from bedrock topography, lead to re-oxidation of previously stored, reduced S. This has been demonstrated using stable S isotope methods (Eimers et al. 2004b) analysis of the... 

The WhiUans-Cassidy model is based on an idealized conception of the interaction of the East Antarctic ice sheet with a mountain barrier. It assumes that the ice sheet is 3 km thick and that the bedrock surface over which it flows is relatively smooth. Actually, we know that the bedrock topography under the ice adjacent to the East Antarctic ice sheet consists of flat-topped mesas that are separated in some cases by deep valleys (Sections 17.3 and 17.4). The rugged subglacial bedrock topography causes meteorite stranding surfaces to form... 

The topography rises towards the east from the coastal area in the west. Half of the study sites are situated in the esker formations and the other half in the basal till areas. The fine-rich tills are mainly composed of quartz, feldspars, amphiboles, chlorites and micas. The sand components are composed of mainly quartz and feldspars and poorly reflect the underlying bedrock (Raisanen etal. 1992). 

One difficulty with this hypothesis for the denudation of the bedrock surface under the Sound is that there are deep basins north of the mapped edge of the cuesta that could not have been excavated by the proposed river system. These are shown by the shaded areas in Fig. 2. They are thought to be formed on the Fall Zone surface but they may be closed off by outliers of Coastal Plain sediments. Some river valleys on the Fall Zone surface have been overdeepened by subsequent glacial erosion (the Quinnipiac River valley both south and north of New Haven contains basins up to 250 m deep, for example), but it is unlikely that the deep areas on the Fall Zone surface could have been formed this way since the shape of the basins is not elongated in the direction of ice flow. More detailed mapping of the topography of the Fall Zone surface under Long Island may help resolve this problem. 

Another example of instability in limestone bedrock is the presence of cavities. The relatively faster dissolution of limestone which gives rise to karst topography creating subsurface cavities that caves in to form sinkholes, as shown in Figure 2.23. 

Fig. 17.5 A band of sediment-laden ice in the Elephant Moraine is covered by clasts and fine-grained sediment that were released by the sublimation of the ice. Such bands of dirty ice can be traced for several kilometers along the length of the moraine and presumably are basal ice that was forced to the surface of the ice sheet by the mountainous topography of the bedrock over which the ice is flowing. The moraine is still forming at the present time depending on the rate of sublimation of the ice. The Elephant Moraine is located at the base of a topographic ramp in the surface of the blue ice area (Photo by G. Faure)...

Fig. 17.8 The subglacial bedrock in the drainage basin of the David Glacier has mountainous topography with elevation differences of up to 1,000 m between peaks ruid adjacent vrilleys. The thickness of the ice that flows over this irregular bedrock surface varies widely from about 1,300 m on the polar plateau to a few hundred meters near the coast. In addition, the surface of...

Fig. 17.22 The topography of the ice sheet adjacent to the Allan Hills is strongly affected by the bedrock at the base of the ice sheet. This profile of the ice sheet indicates that a bedrock ridge over which the ice if flowing forces basal ice to the surface which ablates to form a small supraglacial moraine on the surface of the ice. The Elephant and Reckling moraines probably form in the same way as a result of the interaction between the flow of the ice sheet and the mountainous topography of the subglacial bedrock (Adapted from Faure and Buchanan 1987)...

In the quarry areas mainly rock outcrops are exposed on vertical scarp slopes, whereas gentler slope at hill top, the bedrock is overlain by 3 m-18 m thick slopes wash material as also evident from the Drill holes. It is inferred from the exposures that top 1 m-5 m depth of quartzite would be weathered depending upon the amount of micaceous minerals present and the topography of the area. The general trend of foliation, as observed in and around quarry area varies from N20°E to N50°E with 10° to 30° dip towards SE direction. The details of discontinuities of rock mass are summarized in Table 1. 

Site selection depends on the geology, topography, accessibility, and noise. It is preferable to install seismometers in solid bedrock, but volcanoes are typically comprised of layers of ash, flow deposits, and boulders. Repeaters may be required on ridges to rebroadcast signals or boost them if transmitting over tens of kilometers, but represent additional expense and... 

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