Question

Give two examples of natural features that create temporary base levels. Why are they temporary?

Short answer

Natural lakes and resistant rock formations create temporary base levels. They are temporary due to changes from erosion or sedimentation.

Step-by-step solution

Understanding Base Level Concept

The base level is the lowest point to which a river or stream can erode its bed. Generally, the ultimate base level is the sea level. However, there are temporary (or local) base levels that exist above sea level and are subject to change.

Identifying Natural Features

Natural features that create temporary base levels generally include any obstruction or change in the course of a river or stream which slows or stops erosion temporarily. Examples include natural lakes and resistant rock formations.

Example 1: Natural Lakes

Natural lakes can serve as temporary base levels. For instance, a river flowing into a lake will have its erosive power reduced, as the lake serves as a base level until the river continues beyond the lake. These lakes might dry up or get filled with sediment over time, making them temporary.

Example 2: Resistant Rock Formations

Resistant rock formations, like a layer of hard bedrock, can act as a temporary base level. Rivers erode the less resistant layers faster, leading to a waterfall or a steep section of the river. Once the hard layer is eroded away, the base level changes, making these features temporary.

Analyzing Temporariness

These features are considered temporary because they are subject to geological changes over time. Erosion, sedimentation, and tectonic activities can alter or remove them, resulting in a change to the river's base level, which moves higher or lower depending on new conditions.

Key concepts

Temporary Base Levels

Temporary base levels refer to geological features within rivers or streams that limit their erosion temporarily. Unlike the ultimate base level, which is usually the sea level, temporary base levels are found at higher elevations and can shift over time. They affect how a river or stream progresses by reducing their erosive force at specific points.

• They often result from natural actions or geological structures that obstruct the natural flow.
• Being temporary, these features will eventually give way to continuing erosion or geological change.

This temporary nature results from factors like natural wear, sediment buildup, or changes in river courses. Understanding these dynamic base levels helps us comprehend how landscapes evolve over time.

River Erosion

River erosion is the process of wearing away riverbeds and banks caused by flowing water. It significantly shapes landscapes and can be influenced by various natural features along the river's course. Rivers possess the energy to cut into the land, transporting sediment downstream.

• The potency of river erosion decreases when a river meets temporary base levels like lakes or resistant rock formations.
• While rivers aim to reach their ultimate base level, interventions create temporary stops or shifts in their erosive progress.

Factors such as water velocity, volume, and the geological characteristics of the river's path all influence erosion. Understanding these factors can explain how temporary base levels can alter the natural erosive cycle.

Natural Lakes

Natural lakes serve as temporary base levels by obstructing the flow of rivers, reducing their erosive power significantly. They act as basins into which rivers flow, and while the water pauses before continuing its path, the sediment carried by the river often settles.

• Rivers lose energy and velocity as they enter lakes, which reduces erosion significantly.
• These lakes can change over time, by either becoming filled with sediment or losing water due to evaporation, thus altering the river's base level.

Lakes' temporary nature arises from their susceptibility to climatic and environmental changes. Capturing this dynamic helps illustrate the temporary aspects of these geological features.

Resistant Rock Formations

Resistant rock formations create temporary base levels by acting as natural barriers in the river course. These formations usually consist of hard, less erodible rock that temporarily halts the downward erosion of a river's bed.

• Common examples include cliffs or sections of bedrock that result in waterfalls or rapids.
• These features alter the river's path or create abrupt drops, creating a temporary halt in erosion.

Over time, even resistant rocks can erode, leading to changes in the river's path and base level. This showcases the temporary but impactful role of these structures in river ecology and landscape development.