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### ANSWERS

17-1: Using remote sensors: in chemistry, information on the composition of the atmosphere can be quantitatively assessed; in physics, the radiation laws discussed in the Introduction section can be tested; in botany, the distribution of major plant categories can be determined; and in geography, the precise outlines of coastlines and of river courses can be mapped. Many other answers are possible. BACK

17-2: Look for the "Henry Mountains" in larger type, in the lower right corner. The Waterpocket Fold is to their left (labelled in small type). Much of what was shown in Section 2 of this fold is present in the sketch map. BACK

17-3: Quite similar. Both tectonic regimes involve plate collisions. BACK

17-4: The chief difference is the absence of well-defined ridges that rise above lower valleys, thus helping to outline the folding (the ridges in the Anti-Atlas and Pakistan scenes are hard, resistant sedimentary rocks that stand above the more easily eroded softer rocks in the valleys). In this Arabian Shield, most of the rocks have been metamorphosed into units that have much less variability in erosive resistance, so that ridges don't develop. There are some areas in which banding creates a crude allusion of ridges. But, overall, this scene is typical of the topographic expression of shield terranes. BACK

17-5: The Pilbara block is much like a shield and, in fact, consists of typical shield crystalline rocks. The lower half of the image consists of sedimentary rocks (mainly) in structurally deformed basins; there are, however, few prominent ridge forms as are characteristic of fold belts. BACK

17-6: The Mauna Loa (Hawaiian) structure is a basaltic shield volcano; it has numerous dark basalt flows extending down its sides. The Java volcanoes are andesitic in composition (higher silica; less iron) and lavas emanating from them are intermediate to light in color tone; these do not stand out visually in contrast and are hard to see at all in the Landsat image. BACK

17-7: The word "dendritic" has a Greek root. It refers to a tree and its branches. Dendritic drainage has a master stream (the tree "trunk"), with tributaries (the branches) that themselves are fed by even smaller streams (the twigs on the branches). BACK

17-8: The Ganges delta is huge, being almost two Landsat scenes wide. There have been many individual river distributaries (including from other rivers, such as the Hoogly River passing by Calcutta on the left of the image) that have built up the shore deposits over millions of years. The delta deposits have been dissected both currently and in the past by these distributaries (in the mangroves they are tidal estuaries) which have produced through back erosion the fingerlike peninsulas that extend to the coastline. In contrast, the Yukon delta has only a few distributaries that have yet to carve up the fanlike shape of the main delta. Neither delta is presently producing "birds-foot" extension deposits. BACK

17-9: The fjord waterways are part of the famous inland passage through the Alaskan Panhandle and are frequented by many pleasure cruise ships (the "Alaskan Cruise" so commonly promoted in the Travel pages of newspapers and magazines) each late spring to fall. This brings tourism to the ports of call such as Juneau. BACK

17-10: Over the short run, the islands are quite vulnerable to hurricanes and "Nor'easters". In addition to direct wind damage, maximized because so few trees are on the islands, the winds push the waves onto the islands, which are at most just a few tens of feet above sea level, and inundate beaches and homes built near them. Over the long haul, these islands may both be shifted by natural wave action and be gradually submerged if sea level continues to rise worldwide. BACK

17-11: Caves. Most caves are made by dissolving limestone with water (usually slightly acid from CO2 within it). Sinkholes are formed at the surface in a similar manner (many sinkholes enlarge into caves below). This part of China also has numerous caves. BACK

17-12: Lakes are depressions that fill with water. The advance or retreat of ice in one general direction can lead to gouging out of stretched-out depressions that receive water after the glaciers retreat. On a grand scale, the Great Lakes are the classic example, although these are not aligned. Alignment can occur in mountain glaciers in which the preglacial streams all flowed off the crest in one general direction. These lakes in Alaska are a good example:

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17-13: They will eventually fill up with more salts and most probably then with sediments that cover them. Lakes, in general, are transient geologically and disappear as they are filled and streams wander elsewhere to lower elevations, often forming lakes at their termini if the drainage is interior (i.e., doesn't reach an ocean). BACK

17-14: Yes, although this is not common. If vegetated, the cover is mainly grasses and specialized plants and perhaps small trees that do not need clay-rich soil to root and grow. About 90% of the world's desert biomes are not dominated by sand dunes; in fact, a wide variety of plant life adapted to low annual rainfall is characteristic of most deserts. In the U.S., the Sand Hills of Nebraska consist in part of dunes made up of sand and silt (derived from winds carrying glacial dust from the deposits to the north), formed during a time in the past (younger than 10000 years) where that region's climate was even drier; now, semi-arid conditions there foster partial cover with grasses. Here is a Landsat TM subscene of the Sand Hills that confirms the presence of grasslands, developed mainly in the lowlands or hollows between these linear dunes (which make up the largest dune field in North America).

Another example of dunes supporting vegetation is found in the Kalahari Desert in Namibia. Here dunes are migrating northward, overriding natural vegetation and farms, leaving some growth to still persist as more sand continues to move to the grasslands beyond the image top.

Sand dunes along oceanic beaches are often stabilized by vegetation indigenous to that ecology. BACK

17-15: The glaciers themselves, when gone, would leave behind wide valleys whose cross-sectional profiles are U-shaped. The high mountains, from which the glaciers emanate, would be rugged, with steep angular slopes and thin ridges, having a topography much like the high Alps of Europe. BACK

17-16: This is a thought exercise and requires no direct answer. BACK

17-17: Again, a subjective action on your part. BACK

17-18: There are many more ridges in the Elk terrane. These are closer spaced, hence the slopes are less wide (probably steeper) and the valley floors are narrow. BACK

17-19: Clearly, the Elk terrane is higher than Sixes River. A large area of the Elk terrane is above 3000 ft whereas the Sixes River has only a moderate area as high as 2000-2500 ft. BACK

17-20: Much of western Oregon is heavily forested and is a major source of timber. The squares are classic examples of the type of deforestation by clear-cutting that is carried out by the lumber industry. This is a significant part of the economy of this region. BACK

17-21: It's subtle, but there appears to be a slighly closer spacing of ridges in the Yolla Bolly terrane compared with the Rogue Valley terrane. BACK

17-22: Ridge density and ridge orientation, and to a lesser degree, hypsometric curves and maximum elevations. BACK

17-23: The chief use of space imagery is that it provides a visual overview of differences in landforms/topography expression; it helps to pinpoint areas for quantitative analysis by conventional morphometric means. As stereo imagery becomes more common from spaceborne sensors, or elevation measurements are obtained by systems such as SRTM, the ability to make measurements now restricted to topographic maps will notably expand the use of images acquired from satellites or astronaut photography. BACK