Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Weathering / Physical weathering: frost cracking, thermal stress and root wedging
Physical weathering: frost cracking, thermal stress and root wedging
Mechanical breakdown of rock without chemical change: water freezing in cracks, repeated heating and cooling, and growing roots. It multiplies reactive surface area (a 1 cm cube split into 1 mm cubes gains 10 times the area).
Boundary: where this process starts
Starts with: Water enters joints and pores of rock
Boundary: where it ends
Ends after: Rock fragments and fresh mineral surface area increase
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
- Participant
- Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
- Resource
- Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
- Step
- One thing that happens in a process. Every step has at least one participant and carries evidence.
- Decision fork
- A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
- Loop
- A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
- Size of impact
- Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
- Evidence
- The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
- Boundary
- Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
- Subprocess
- A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
- Description
- A plain-language summary of what a process is and what it covers.
- Hypothesis
- A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.
Every step, with its evidence
The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.
Water enters joints and pores of rock
Evidence (1) · added by Quanta
- Matsuoka 2001, Microgelivation versus macrogelivation: towards bridging the gap between laboratory and field frost weathering, Permafrost and Periglacial Processes, doi:10.1002/ppp.393: Moisture supply is the limiting control on frost weathering. (confidence 0.55)
Freezing in the -3 to -6 C window grows ice lenses (about 9 percent volume expansion)
Evidence (1) · added by Quanta
- Matsuoka 2001, Microgelivation versus macrogelivation: towards bridging the gap between laboratory and field frost weathering, Permafrost and Periglacial Processes, doi:10.1002/ppp.393: Ice segregation in the frost-cracking window of about -3 to -6 C is the dominant mechanism in many rock walls; freezing water expands about 9 percent. (confidence 0.6)
⑂ Dominant physical agent
Evidence (1) · added by Quanta
- Matsuoka 2001, Microgelivation versus macrogelivation: towards bridging the gap between laboratory and field frost weathering, Permafrost and Periglacial Processes, doi:10.1002/ppp.393: Relative importance of frost, thermal stress and roots varies by climate; shares are estimated. (confidence 0.35)
Roots wedge into cracks and widen them
Evidence (1) · added by Quanta
- Brady and Weil, The Nature and Properties of Soils (15th ed.), chapters on soil water and soil formation (textbook, no DOI): Root growth pressure fractures weak rock; textbook soil formation. (confidence 0.5)
Daily temperature swings of 20-50 C fatigue mineral grains
Evidence (1) · added by Quanta
- Matsuoka 2001, Microgelivation versus macrogelivation: towards bridging the gap between laboratory and field frost weathering, Permafrost and Periglacial Processes, doi:10.1002/ppp.393: Thermal stress is a secondary contributor in many cold and arid sites. (confidence 0.4)
Rock fragments and fresh mineral surface area increase
Evidence (1) · added by Quanta
- Brady and Weil, The Nature and Properties of Soils (15th ed.), chapters on soil water and soil formation (textbook, no DOI): Fragmentation raises surface area for chemical weathering. (confidence 0.6)