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Difficulty: MediumWeathering and Mass Wasting Processes

In alpine and high-latitude environments, mechanical weathering continuously alters exposed rock slopes through freeze-thaw action. Arrange the following sequential stages of frost wedging in the correct chronological order from initial water accumulation to final downslope accumulation.

  1. 1Meltwater infiltrates pre-existing joints, fractures, and pore spaces within exposed rock faces during periods above freezing point.
  2. 2Ambient temperatures fall below 0°C, causing the trapped water within rock fractures to freeze into ice.
  3. 3Ice expansion exerts intense volumetric pressure outward against the surrounding joint walls of the rock.
  4. 4Repeated diurnal freeze-thaw cycles cause the joint lines to enlarge until Angular rock fragments detach completely and accumulate at the base as scree or talus.

Answer

The correct chronological sequence of frost wedging starts with meltwater infiltration into rock fractures, followed by freezing as temperatures drop, volumetric expansion exerting outward pressure on joint walls, and culminating in repeated freeze-thaw cycles splitting the rock into scree at the mountain base.
Frost wedging follows a precise physical progression: liquid water infiltrates open joint lines, freezes when temperatures fall below 0°C, expands by ~9% in volume to exert immense pressure on surrounding rock walls, and ultimately fractures the rock completely over repeated cycles to form scree deposits at the base.

Step-by-Step Solution

1
Identify the initial process leading to frost wedging.
Liquid meltwater must first enter pre-existing cracks and joints within exposed rock surfaces during daytime or warmer seasons.
Without liquid water infiltration into rock voids, freeze-thaw action cannot initiate.
2
Determine the thermal change leading to phase transition.
Temperatures drop below the freezing threshold (0°C), converting the trapped water into ice.
Cooling is necessary for the phase change from liquid water to solid ice within the confined space.
3
Analyze the mechanical stress generated by the phase change.
Water expands by about 9% upon freezing, generating heavy outward lateral pressure against internal rock walls.
The volumetric expansion of ice directly generates mechanical stress within rock joints.
4
Identify the cumulative landform result of repeated stress.
Frequent oscillation around freezing point breaks jointed blocks apart, causing them to fall downslope to form talus/scree slopes.
Repeated stress cycles eventually overcome rock cohesion, resulting in fragment detachment and gravity-driven accumulation.

Key Concept

Frost Wedging Mechanics and Scree Formation
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Topics

Weathering and Mass Wasting Processes

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