Geomorphology: A River’s Work is Never Done (PCEC)
This lesson will explain the features of a river system and landscape features created by rivers including meander-scrolls, oxbow lakes and abandoned channels. Once the processes are understood, participants can determine the relative age of features from an aerial photograph.
4 and up
Indoor or outdoor classroom
Potlatch Conservation Education Center at Cook’s Lake, Casscoe
Education Program Coordinator, 870-241-3373
30 minutes to an hour
Suggested Number of Participants:
20 - 25
One adult supervisor per 10 students; outdoor activities, weather permitting.
- Learn how water sculpts landscape features and how these processes formed Cook’s Lake and its surrounding landscape.
- Learn to determine relative ages of landscape features based on river processes and logic.
- Understand the landscape relationship among Cook’s Lake, its wetlands and the White River.
*See glossary for definations
½ cup each of sand, clay and loam
Three jars or liter bottles
Geomorphology is the study of how landscapes are formed. For Cook’s Lake, all landscape features were formed by water, thus their study could be called fluvial geomorphology. As water flows through an area, it moves sediment, which accounts for erosion and sediment deposits.
- Water’s ability to erode and deposit sediment can be illustrated with a few jars or two-liter bottles. Place 1/2 cup of sediment in each, preferably using different weight/size classes such as sand, silt and clay. Use a ruler to measure how deep the sediment is in the jar.
- Add water so that each jar is about 3/4 full and cap the container. Swirl the water in the jars by shaking the jar until the sediment is picked up in the water column. This represents water’s sediment erosion as its velocity increases.
- Set the jar down and see how long it takes to settle. This is deposition. As the water velocity becomes still, the sediment is deposited on the floor of the jar. Large heavy particles settle first, followed by finer sediments such as silts, and finally the clays will settle last.
- Ask participants to record the amount of time it takes for the different sediment types to settle. Measure the sediment depth after the water appears clear to make sure that all of the sediment has been deposited. (The jar containing the clay particles may take a long time to settle.)
- Briefly discuss geomorphic concepts that will be observed later in the field study and go over the vocabulary words to be sure participants understand the terminology before proceeding to the field study.
- Go over the following prior to the field trip:
- The basic layout of Cook’s Lake and its wetlands on a map
- The geomorphic concepts introduced in the classroom, especially the formation of meander-scroll topography and oxbow lake cutoffs
- The relative ages of the four surfaces in the Cook’s Lake area
- Basic map skills
- Before going into the field, stand at the lodge looking over Cook’s Lake. Ask the participants to decide if the land on the other side of the lake is higher or lower than the land where they stand. Why is this?
- Hand out copies of the participant worksheet: Cook’s Lake Map .Have them label the four areas (see white lines on the map) from oldest (1) to youngest (4). Circle areas on the photo that look like meander-scroll topography.
- Have participants mark their approximate field location on the map. Are there any features that look like meander-scroll topography on the ground?
- Ask participants to examine the area where they are standing and respond to the following:
- Are there any signs of sediment deposits on leaves or on the ground?
- Is the area where participants are currently standing experiencing erosion or deposition? Why or why not?
- Will Cook’s Lake erode the ridge on which Potlatch Conservation Education Center sits, causing the lodge to fall 50 feet into the lake? Why or why not?
- Return to the classroom with data to compare notes and conclusions.
- Using the data collected, decide which part of the lake is the oldest and the youngest.
- Is the Cook’s Lake area experiencing large-scale erosion or deposition?
- What are the long-term effects of erosion or deposition around Cook’s Lake?
Decomposition – biological process by which dead materials are broken down into simpler forms of matter
Erosion – the natural process by which the surface of the earth is worn away by the action of water, glaciers, winds, waves, etc
Fluvial geomorphology – study of the processes and pressures on river systems
Geomorphology – study of landforms and the processes that shape them
Meander-scroll – one of a series of long, parallel, closely fitting ridges and troughs along the inner bank of a stream meander (curve, bend, loop or turn) formed as the channel migrates toward the outer bank; also a small, elongated lake occurring on a flood plain in a well-defined part of an abandoned stream channel
Oxbow lake – a crescent-shaped body of water formed when a wide meander of a river is cut off from the main channel
Terrace – a flat, narrow stretch of ground having vertical or sloping sides and a flat top