The following questions are based on Map T-6, the “Johnson City, Tennessee-Virginia- Kentucky-North Carolina,” topographic map (scale 1:250,000; contour interval 100 feet). This map shows a portion of the Appalachian Mountains at the Tennessee, Kentucky, and Virginia border (36°39?30?N, 83°01?05?W). Figure 41-4 is a satellite image of this same region (to view this image, go to the Hess Labs Media Website and Exercise 41). 1. (a) Describe the general topography in the region north of Poor Valley Ridge. (b) What kind of stream drainage pattern has developed here? (c) How has the road system been influenced by the topography? 2. (a) Describe the general topography of the region between Clinch Mountain and Powell Mountain. (b) What kind of stream drainage pattern has developed here? (c) How has the road system been influenced by the topography? 3. (a) The Powell River has a meandering pattern. Is it flowing across a flat floodplain? (b) How do you know? The following questions are based on Map T-2, the “Umnak, Alaska,” topographic map (scale 1:250,000; contour interval 200 feet). 4. 5. What kind of drainage pattern has developed around the outside of the Okmok Caldera? What kind of drainage pattern has developed inside the Okmok Caldera? 287
The Correct Answer and Explanation is:
1. (a) The region north of Poor Valley Ridge has gently rolling to moderately hilly topography with broad valleys and low ridges.
(b) The stream drainage pattern is dendritic, indicating uniform rock resistance and horizontal or gently dipping strata.
(c) The road system follows the valleys and avoids steep slopes, often paralleling streams and crossing ridges at low points (gaps or saddles).
2. (a) Between Clinch Mountain and Powell Mountain, the topography is rugged and mountainous with narrow, steep-walled valleys.
(b) The stream drainage pattern is trellis, which forms in folded terrain where streams run parallel in valleys and join at right angles.
(c) Roads are limited to valley floors and gaps due to steep, rugged terrain, indicating topography strongly controls transportation routes.
3. (a) Yes, the Powell River meanders across a broad, relatively flat floodplain.
(b) The evidence comes from the river’s sinuous path and wide bends, which are typical of streams flowing on flat land with low gradient.
4. Around the outside of the Okmok Caldera, the drainage pattern is radial, typical of volcanic cones where streams radiate from a central high point.
5. Inside the Okmok Caldera, the drainage pattern is centripetal, with streams flowing inward toward the central depression or basin.
Explanation
The topographic features of mountainous regions significantly influence drainage and road development. North of Poor Valley Ridge, the land is gently rolling with minor relief, allowing dendritic drainage—a tree-like pattern where tributaries join main streams irregularly. This suggests homogeneous rock types and less structural control. Roads here take advantage of the easier terrain, often following river valleys for smoother grades.
Between Clinch Mountain and Powell Mountain, the land is shaped by folding and differential erosion, forming parallel ridges and valleys. This terrain produces a trellis drainage pattern, where main streams follow synclinal valleys and tributaries join perpendicularly from steep slopes. Such topography restricts road construction to valleys and gaps, making the road system discontinuous and influenced heavily by landform constraints.
The Powell River shows a classic meandering pattern, indicating low gradient and a broad floodplain. Meandering rivers typically develop in areas with soft sediments and low relief, as confirmed by the river’s looping bends and wide valley floor seen on the map.
In volcanic landscapes like Umnak Island, drainage reflects volcanic morphology. Around Okmok Caldera, radial drainage develops as water flows downslope in all directions from the summit, while inside the caldera, the enclosed basin causes water to converge inward, forming centripetal drainage. These patterns clearly reflect the structural origin of the terrain—the cone-like structure of the volcano and the collapse basin of the caldera.
These observations demonstrate how geology and topography shape both natural drainage and human infrastructure.
