The Nalley Valley, unlike most valleys or canyons, has very little water flowing
ID: 233884 • Letter: T
Question
The Nalley Valley, unlike most valleys or canyons, has very little water flowing through it. There is some, but not much. Geologists call streams that are really small compared to the valley that they flow through. "underfit". The implication is that the stream couldn't have carved the valley through erosion; it's too small. Answer the following questions based on the Pleistocene ice ages lecture and the Puget Sound glaciation lecture, plus additional individual research where necessary. Use appropriate geomorphological terms in your answer.
1) Describe the shape of Nalley Valley from its origin near I-5 to near where it peters out down by S 82nd St. Is the shape reminiscent of any other natural shape relating to hydrologic process?
2) Relate the presence of the Nalley Valley to the recent glacial history of this area. In your explanation address why the Nalley Valley appears to start out of thin air near I-5. Most valleys start out narrow and get wider downstream. The Nalley Valley doesn't do this; it starts out wide. Why?
Hint: The Nalley Valley is located in Washington state.
Explanation / Answer
N Polar view of Earth between 22 – 15 ka showing ice sheets and sea level reduce by ~120 m North American Ice Sheets Last Glacial Period (ca. 20,000 yrs ago). How do we know that we have been in an Ice Age for ~2 Myrs?(a) Evidence of: 1. Glacial Erosion 2. Glacial Sediments 3. Glacial Landforms Climate Since the Cenozoic (65 Ma to today) Glacial Cycles Within an Ice Age Seattle Area Shows Evidence for 7? Glacial Advances Drift = any deposit of a glacier Glacial Sediments in Puget Sound the Nalley Valley is one of Tacoma's major industrial areas. The main drag is South Tacoma Way, which was the main north-south corridor before Interstate 5 was built. It is currently home to companies such as Tacoma Screw, Atlas Foundry, Parker Paint and Tacoma Power. Bob's Java Jive, a well-known dive bar shaped like a coffee pot, is located in this neighborhood. The topography and near-surface geology of the study area is largely the product of the last glaciation (Vashon). The Vashon glaciation left a prominent pattern of north-trending ridges and swales as the glacial ice crossed the upland plateau, and left deposits of sand and gravels that mantle the upland surface. The Vashon and older deposits in the Tacoma area form a sequence of permeable sand and gravel layers separated by finer-grained layers of clay and silt or other low permeable soils, which are exposed in places along the steep slopes that border the upland plateau. The Vashon and older deposits comprise several aquifers (a geologic formation that contains sufficient saturated permeable material to yield water to wells and springs) and aquitards (geologic formations that may contain groundwater but are incapable of transferring that water to a well or spring) within the subsurface, which control subsurface water movement from the upland to the lowland as well as the locations of streams and creeks that occupy former outwash channels