Question

Mass wasting is influenced by many processes associated with all four spheres of the Earth system. Select three items from the list below. For each, outline a series of events that relate the item to various spheres and to a mass- wasting process. Here is an example that assumes "frost wedging" is an item on the list: Frost wedging involves rock (geosphere) being broken when water (hydrosphere) freezes. Freeze-thaw cycles (atmosphere) promote frost wedging. When frost wedging loosens a rock on a cliff, the fragment tumbles to the base of the cliff. This event, called a rockfall, is an example of mass wasting. Now you give it a try. Use your imagination. a. Wildfire b. Spring thaw/melting snow c. Highway road cut d. Crashing waves e. Cavern formation (see Figures 5.42 and 5.43 )

Short answer

Wildfires, spring thaws, and highway road cuts lead to mass wasting by destabilizing soil and rock, influenced by interactions among the geosphere, hydrosphere, atmosphere, and biosphere.

Step-by-step solution

Select Item - Wildfire

Wildfire affects various spheres of the Earth system. It starts with the biosphere, as wildfires commonly burn through vegetation. The atmosphere gets involved by providing the oxygen necessary for combustion and carrying smoke and particulates. The geosphere is impacted when the intense heat from wildfires may cause the soil to become dry and prone to erosion. Lastly, the hydrosphere can be affected as vegetation loss can lead to increased runoff during rainfall events, thereby promoting mass wasting events like mudflows.

Connect Wildfire to Spheres and Mass Wasting

After a wildfire, the lack of vegetation weakens soil stabilization, increasing vulnerability to erosion. When the atmosphere introduces rainfall, the absence of plant roots leads to significant water infiltration and runoff (hydrosphere), resulting in soil saturation. The saturated, unstable soil may lead to mudflows (mass wasting) as it moves down slopes.

Select Item - Spring Thaw/Melting Snow

During spring thaw or melting snow, interactions among various spheres are evident. This involves the atmosphere warming temperatures causing snow to melt. The hydrosphere plays a role as the snowmelt contributes to increased water flow. The geosphere is impacted by this increased water which may infiltrate the soil, causing mass movements like landslides or slumping.

Connect Spring Thaw to Spheres and Mass Wasting

As snow melts, excess water increases soil saturation. The geosphere's stability is compromised as the soil structure weakens, resulting in potential mass wasting events. Landslides might be triggered on slopes as the water content increases beyond the soil's cohesive strength, causing gravitational downslope movement.

Select Item - Highway Road Cut

Highway road cuts directly affect the geosphere by disrupting the natural slope of terrain, sometimes steepening it beyond stable angles. The atmosphere can contribute through weather conditions such as rain or freeze-thaw cycles, adding further stress to the cut. Vegetation (biosphere) may be removed or insufficient to anchor the new slope.

Connect Highway Road Cut to Spheres and Mass Wasting

In a road cut setting, the disturbed geosphere without natural support becomes prone to gravitational failures like rockfalls or slumps. Rain (atmosphere and hydrosphere) can exacerbate this by infiltrating newly exposed rock surfaces, freezing, or chemically interacting with the rock to weaken its integrity. This leads to mass wasting events when the rock fails or the slope gives way.

Key concepts

Earth system spheres

The Earth is divided into four major spheres that interact continuously. These spheres are crucial in processes like mass wasting, which is the movement of soil and rock down slopes due to gravity. Understanding how these spheres interact helps us grasp the complexities of Earth's surface processes.
Each sphere plays a distinct role:

• Geosphere: This includes all the earth materials such as soil, rocks, and landforms. It is directly involved in mass wasting since slope stability depends on the type and arrangement of geological materials.
• Biosphere: Comprising all living organisms, the biosphere influences mass wasting by stabilizing soil through plant roots which reduce erosion and promote water absorption.
• Hydrosphere: This sphere entails all water bodies, and it's heavily involved in processes like erosion and weathering, which can lead to or exacerbate mass wasting.
• Atmosphere: The gaseous layer surrounding Earth, the atmosphere mainly affects mass wasting through weather patterns, temperature, and climatic conditions like precipitation and storms.

geosphere

The geosphere plays a foundational role in the study of mass wasting. It encompasses all the rocks and sediments that make up the Earth's crust, providing the material that can be moved by gravity-driven slope processes.
Rock and Soil Interaction: The type of rock and soil in an area greatly affects its susceptibility to mass wasting. For instance, clay-rich soils might become slippery when wet, promoting landslides, whereas rocky outcrops might allow for rockfalls if weathering destabilizes the surface.
Mass wasting examples:

• Landslides: Triggered when sloped earthen materials lose stability.
• Slumps: A rotational movement of soil and rock layers along a curved surface.
• Rockfalls: Commonly occur in mountainous regions where loose rocks tumble downwards.

The geosphere is the canvas on which all other spheres paint their impact, resulting in dynamic changes in landscape and structure.

biosphere

Plants and other organisms within the biosphere significantly influence mass wasting processes. Vegetation plays a critical role in anchoring soil and reducing erosion, making it a natural defense against mass wasting events.
Vegetation as Soil Stabilizers: Plant roots hold soil in place, absorbing water and reducing the likelihood of water-induced mass wasting like mudslides.
Wildfires and Impact: When wildfires occur, they devastate vegetation, removing this crucial stabilizing factor. Following a wildfire, the soil becomes vulnerable to erosion and mass wasting since there are no roots to hold it together.
In areas with rich vegetation, the rate of mass wasting events is usually lower. Conversely, deforestation or the loss of plant life due to natural disasters tends to increase such events, underscoring the biosphere's impact on soil stability.

• Role of animal activity: Burrowing animals can also destabilize slopes, occasionally leading to ground subsidence or small landslides.

hydrosphere

Water is a powerful force in shaping Earth's surface, making the hydrosphere a key player in mass wasting. All forms of water—from rivers and lakes to underground aquifers and rain—affect the stability of the geosphere.
Role of Water in Mass Wasting: Water contributes to mass wasting primarily through processes like weathering, erosion, and increasing soil moisture, which destabilizes slopes.

• Saturation and Stability: Excessive rainfall or snowmelt can saturate soil, reducing friction and increasing the chances of landslides.
• Erosion and Flow: Streams can undercut banks, leading to collapse, while coastal erosion can cause cliffs to retreat.
• Groundwater Impact: Rise and fall of the water table can affect the pressure in soil pores, leading to shifts and potential slumps.

The hydrosphere, therefore, plays a dual role in both nourishing ecosystems and, paradoxically, enabling potentially destructive mass wasting events.

atmosphere

The atmosphere contributes to mass wasting primarily through weather conditions and climate. It influences precipitation, temperature changes, and wind—all of which can impact the stability of the Earth's surface.
Weather Patterns and Mass Wasting: Rainfall from the atmosphere can trigger landslides by saturating the soil, especially after intense storms.
Freeze-Thaw Cycles: These cycles entail water entering cracks in rocks and freezing, which expands and exerts pressure on the rock. Repeated freeze-thaw cycles can weaken rock structures, eventually leading to rockfalls.
While the atmospheric conditions are not direct agents of mass wasting, their role in weathering processes and hydrosphere interactions makes them vital in understanding how and when mass wasting occurs. Whether it's through heavy rainfall leading to flash floods or changes in temperature promoting frost wedging, the atmosphere is a critical factor influencing these geological processes.