USA River Terraces Quiz
Incision, uplift, climatic controls (10 questions).
USA River Terraces Quiz: Quick Study Notes
River terraces are fascinating geological features that reveal much about the Earth’s dynamic past, particularly in regions shaped by active tectonics and fluctuating climates. In the USA, many major river systems exhibit impressive terrace sequences, offering a chronological record of landscape evolution. This quiz delves into the key processes of incision, uplift, and climatic controls that govern their formation.
Key Concepts
The primary process where a river cuts vertically downward into its bed, often leaving older floodplains elevated as terraces.
The geological rising of landmasses due to plate tectonic forces, which increases stream gradient and enhances river incision.
Changes in climate, such as glacial-interglacial cycles, alter precipitation, discharge, and sediment load, influencing a river’s erosional or depositional regime.
Categorized by their formation: Paired (symmetrical, rapid incision), Unpaired (asymmetrical, lateral migration), Strath (cut into bedrock), and Fill (cut into alluvium).
Key Takeaways
- River terraces are remnants of former floodplains, now elevated above the active river channel.
- Their formation is fundamentally driven by periods of net river incision into its valley.
- Tectonic uplift provides the necessary gradient for rivers to maintain or increase their erosive power over long timescales.
- Fluctuations in climate, particularly during the Quaternary, can cause rivers to switch between erosional (incision) and depositional phases, leaving behind terrace sequences.
- Changes in base level (e.g., sea level changes, lake levels) also play a crucial role in triggering incision and terrace formation.
- The study of river terraces helps reconstruct past landscapes, tectonic activity, and paleoclimates.
Frequently Asked Questions
What are river terraces?
River terraces are step-like landforms found along the sides of river valleys. They represent abandoned floodplains that were previously occupied by the river, but have since been elevated as the river incised (cut downwards) into its bed.
How does river incision lead to terrace formation?
River incision is the process where a river cuts vertically downward into its channel. If this incision is sustained over time, the river abandons its current floodplain at a higher elevation, forming a terrace, and establishes a new, lower floodplain.
What role does tectonic uplift play in creating river terraces?
Tectonic uplift raises the land surface relative to base level, increasing the potential energy of the river. This increased gradient provides the river with more erosive power, promoting deeper and more sustained incision, which in turn leads to the formation of higher and more numerous terraces.
How do climatic changes affect river terrace development?
Climatic changes, such as glacial-interglacial cycles, significantly alter a river’s discharge and sediment load. During periods of increased discharge (e.g., melting glaciers) or reduced sediment supply, rivers tend to incise. Conversely, increased sediment supply (e.g., periglacial weathering) can lead to aggradation (deposition), setting the stage for subsequent incision and terrace formation.
What are the main types of river terraces?
The two main types are strath terraces and alluvial (or fill) terraces. Strath terraces are bedrock surfaces covered by a thin layer of alluvium, formed when a river cuts into bedrock. Alluvial terraces are formed when a river cuts into its own previously deposited alluvium (sediment fill).
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