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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Aggregate formation and pore structure / Freeze-thaw cycling and soil structure

Freeze-thaw cycling and soil structure

How repeated freezing and thawing and ice lens growth break or reorganise soil aggregates and pores.

Boundary: where this process starts

Starts with: Pore water freezes and expands about 9%

Boundary: where it ends

Ends after: Soil water content at freezing; Frost loosens dense surface soil and creates fine seedbed tilth

PARTICIPANTSRESOURCESFrostIce lensesSoil aggregatesSoil microbesSoil waterOtherparticipantsWaterIceSoil aggregatesPore spaceDissolvedorganic carbonImpact +2 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.Impact 02 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.40% wet (near saturation)Impact +2 of 5. Click for details and evidence.40% moderateImpact 01 of 5. Click for details and evidence.20% dryImpact -2 of 5. Click for details and evidence.↻ balances · moderate · 0.3Impact +2 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.↻ reinforces · weak · 0.2Impact +2 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.Pore water freezes and expands about 9%: uses up Wateruses upPore water freezes and expands about 9%: makes IcemakesUnfrozen water migrates to the freezing front and grows ice lenses: uses WaterUnfrozen water migrates to the freezing front and grows ice lenses: makes IcemakesIce lenses compress and fracture aggregates along planes of weakness: uses Soil aggregatesIce lenses compress and fracture aggregates along planes of weakness: uses Pore spaceSoil water content at freezing: uses WaterThaw flush: lysed microbes and broken aggregates release carbon and N: makes Dissolved organic carbonmakesFrost loosens dense surface soil and creates fine seedbed tilth: uses Soil aggregatesFrost loosens dense surface soil and creates fine seedbed tilth: makes Pore spacemakesFrozen wet subsoil is near impermeable; spring melt runs off and erodes: uses Waterfreezes and expandsWater: freezes and expandsforms as expandingvolumeIce: forms as expanding volumemigrates to the freezingfrontWater: migrates to the freezing frontgrows as lensesIce: grows as lensescompressed and fracturedalong planesSoil aggregates: compressed and fractured along planescompressed as lensesgrowPore space: compressed as lenses growcontent governs freezingdamageWater: content governs freezing damagereleased by lysedmicrobesDissolved organic carbon: released by lysed microbesbroken into fine tilthSoil aggregates: broken into fine tilthloosened by frostheavingPore space: loosened by frost heavingfrozen subsoil blocksinfiltrationWater: frozen subsoil blocks infiltrationStart: Freeze-thawcycling and soilstructureSTARTStart: Freeze-thaw cycling and soil structureEnd: Freeze-thawcycling and soilstructureENDEnd: Freeze-thaw cycling and soil structurePore water freezes andexpands about 9%📄1Pore water freezes and expands about 9%Unfrozen water migratesto the freezing frontand grows ice lenses📄1Unfrozen water migrates to the freezing front and grows ice lensesIce lenses compress andfracture aggregatesalong planes …📄1Ice lenses compress and fracture aggregates along planes of weaknessSoil water content atfreezing📄1Soil water content at freezingThaw flush: lysedmicrobes and brokenaggregates relea…👍1📄1Thaw flush: lysed microbes and broken aggregates release carbon and NFrost loosens densesurface soil andcreates fine seedb…📄1Frost loosens dense surface soil and creates fine seedbed tilthFrozen wet subsoil isnear impermeable;spring melt runs o…📄1Frozen wet subsoil is near impermeable; spring melt runs off and erodes
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.

Pore water freezes and expands about 9%
FrostSoil waterWaterIce
Evidence (1) · added by Fern
  • Taber 1930, Journal of Geology 38:303 (The mechanics of frost heaving): Water expands about 9% on freezing, but heave is mainly caused by ice lens growth. (confidence 0.7)
Unfrozen water migrates to the freezing front and grows ice lenses
Ice lensesSoil waterWaterIce
Evidence (1) · added by Fern
  • Konrad & Morgenstern 1980, Canadian Geotechnical Journal 17:473: Water is drawn to the freezing front by suction, building segregated ice lenses. (confidence 0.7)
Ice lenses compress and fracture aggregates along planes of weakness
Ice lensesSoil aggregatesSoil aggregatesPore space
Evidence (1) · added by Fern
  • Oztas & Fayetorbay 2003, Catena 52:1: Aggregate stability of wet soils fell with the number of freeze-thaw cycles. (confidence 0.65)
⑂ Soil water content at freezing
SoilWeatherWater
Evidence (1) · added by Fern
  • Edwards 2013, EJSS 64:300: Effect size depends strongly on moisture at freezing; shares are estimates (+-10 points). (confidence 0.45)
Thaw flush: lysed microbes and broken aggregates release carbon and N
Soil microbesSoil aggregatesDissolved organic carbonNitrogenCarbon dioxideNitrous oxide
Evidence (1) · added by Fern
  • Wagner-Riddle et al. 2017, Nature Geoscience 10:279: Freeze-thaw periods accounted for roughly 17-28% of annual cropland N2O emissions in the dataset. (confidence 0.65)
Frost loosens dense surface soil and creates fine seedbed tilth
FrostSoilPore spaceSoil aggregates
Evidence (1) · added by Fern
  • Kvaerno & Oygarden 2006, Catena 67:175: Freeze-thaw changed aggregate size distribution in Norwegian soils, loosening some while weakening others. (confidence 0.55)
Frozen wet subsoil is near impermeable; spring melt runs off and erodes
SnowmeltFrozen soilWaterSediment
Evidence (1) · added by Fern
  • Granger, Gray & Dyck 1984, Canadian Journal of Earth Sciences 21:669: Snowmelt infiltration into frozen prairie soils depends on ice content at freeze-up; wet soils freeze nearly impermeable. (confidence 0.7)