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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Mineral weathering and parent material / Volcanic ash weathering to allophane and imogolite (andic soils)

Volcanic ash weathering to allophane and imogolite (andic soils)

Volcanic glass weathers within centuries in humid climates to nanoscale allophane, imogolite or Al-humus complexes, which give andic soils very low bulk density, high phosphate retention and large organic carbon stocks.

Boundary: where this process starts

Starts with: Volcanic ash (Si-Al-rich glass) is deposited as young parent material

Boundary: where it ends

Ends after: Al-humus complexes form and hold Al so it is not available to precipitate with Si; With drying and Si accumulation allophane converts slowly to halloysite over thousands of years

PARTICIPANTSRESOURCESAllophaneVolcanic ashImogoliteSoil organicmatterAluminumAluminumWaterSiliconSoil organicmatterVolcanic glassImpact +3 of 5. Click for details and evidence.Impact +4 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.45% humus-rich, pH below aboImpact +4 of 5. Click for details and evidence.55% less humus, pH above aboImpact +4 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.↻ reinforces · moderate · 0.3 High water retImpact +2 of 5. Click for details and evidence.Impact 02 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.Volcanic ash (Si-Al-rich glass) is deposited as young parent material: uses Volcanic glassGlass hydrolyses within centuries in humid, well-drained conditions, releasing Al3+ and Si(OH)4: makes AluminummakesGlass hydrolyses within centuries in humid, well-drained conditions, releasing Al3+ and Si(OH)4: uses up Wateruses upGlass hydrolyses within centuries in humid, well-drained conditions, releasing Al3+ and Si(OH)4: makes SiliconmakesGlass hydrolyses within centuries in humid, well-drained conditions, releasing Al3+ and Si(OH)4: uses up Volcanic glassuses upFork: strongly acidic humus-rich soil versus weakly acidic to neutral soil: uses AluminumFork: strongly acidic humus-rich soil versus weakly acidic to neutral soil: uses Soil organic matterAl-humus complexes form and hold Al so it is not available to precipitate with Si: uses up Aluminumuses upAl-humus complexes form and hold Al so it is not available to precipitate with Si: uses up Soil organic matteruses upAl and Si co-precipitate as allophane spherules (about 3.5 to 5 nm) and imogolite tubes (about 2 nm outer diameter): uses up Aluminumuses upAl and Si co-precipitate as allophane spherules (about 3.5 to 5 nm) and imogolite tubes (about 2 nm outer diameter): uses WaterAl and Si co-precipitate as allophane spherules (about 3.5 to 5 nm) and imogolite tubes (about 2 nm outer diameter): uses up Siliconuses upLarge variable-charge surface (several hundred m2 per g) retains over 85 percent of added phosphate and binds organic carbon: uses Soil organic matterOpen allophane aggregates give bulk density below 0.9 g per cm3 and very high water retention: uses WaterWith drying and Si accumulation allophane converts slowly to halloysite over thousands of years: uses WaterWith drying and Si accumulation allophane converts slowly to halloysite over thousands of years: uses up Siliconuses updeposited as parentmaterialVolcanic glass: deposited as parent materialreleased from glassAluminum: released from glasshydrolyses the glassWater: hydrolyses the glassreleased as silicic acidSilicon: released as silicic acidhydrolyses overcenturiesVolcanic glass: hydrolyses over centuriesmobility depends onhumus acidityAluminum: mobility depends on humus acidityhumus-rich soil controlsaluminumSoil organic matter: humus-rich soil controls aluminumbound by humus complexesAluminum: bound by humus complexesbinds aluminum intocomplexesSoil organic matter: binds aluminum into complexesco-precipitates asallophaneAluminum: co-precipitates as allophanehydrates formingallophane structuresWater: hydrates forming allophane structuresco-precipitates asallophaneSilicon: co-precipitates as allophanebound to large surfaceareaSoil organic matter: bound to large surface areaheld in open aggregatesWater: held in open aggregatesdrying drives theconversionWater: drying drives the conversionaccumulates and drivesconversionSilicon: accumulates and drives conversionStart: Volcanic ashweathering to allophaneand imogolite (and…STARTStart: Volcanic ash weathering to allophane and imogolite (andic soils)End: Volcanic ashweathering to allophaneand imogolite (and…ENDEnd: Volcanic ash weathering to allophane and imogolite (andic soils)Volcanic ash(Si-Al-rich glass) isdeposited as you…📄1Volcanic ash (Si-Al-rich glass) is deposited as young parent materialGlass hydrolyses withincenturies in humid,well-drain…📄1Glass hydrolyses within centuries in humid, well-drained conditions, releasing Al3+ and Si(OH)4Fork: strongly acidichumus-rich soil versusweakly acidic …📄1Fork: strongly acidic humus-rich soil versus weakly acidic to neutral soilAl-humus complexes formand hold Al so it isnot available …📄1Al-humus complexes form and hold Al so it is not available to precipitate with SiAl and Sico-precipitate asallophane spherul…📄1Al and Si co-precipitate as allophane spherules (about 3.5 to 5 nm) and imogolite tubes (about 2 nm outer diameter)Large variable-chargesurface (severalhundred m2 per …📄1Large variable-charge surface (several hundred m2 per g) retains over 85 percent of added phosphate and binds organic carbonOpen allophaneaggregates give bulkdensity below 0.9 g p…👍1📄1Open allophane aggregates give bulk density below 0.9 g per cm3 and very high water retentionWith drying and Siaccumulation allophaneconverts slowly …📄1With drying and Si accumulation allophane converts slowly to halloysite over thousands of years
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)
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Volcanic ash (Si-Al-rich glass) is deposited as young parent material
VolcanoesVolcanic ashVolcanic glass
Evidence (1) · added by Fern
  • Shoji, Nanzyo & Dahlgren (1993), Volcanic Ash Soils, Elsevier: Tephra glass has a large surface area and weathers faster than crystalline silicates. (confidence 0.8)
Glass hydrolyses within centuries in humid, well-drained conditions, releasing Al3+ and Si(OH)4
Volcanic ashSoil waterVolcanic glassAluminumSiliconWater
Evidence (1) · added by Fern
  • Shoji, Nanzyo & Dahlgren (1993), Volcanic Ash Soils, Elsevier: Weathering of basaltic to andesitic ash in humid climates forms allophane within decades to centuries. (confidence 0.7)
⑂ Fork: strongly acidic humus-rich soil versus weakly acidic to neutral soil
Soil organic matterAluminumAluminumSoil organic matterHydrogen ions
Evidence (1) · added by Fern
  • Shoji, Nanzyo & Dahlgren (1993), Volcanic Ash Soils, Elsevier: Below about pH 5 with abundant humus, Al is complexed by organic matter (non-allophanic Andosols); above about pH 5 Al and Si co-precipitate as allophane. Shares are an estimate (range 35 to 60 percent). (confidence 0.4)
Al-humus complexes form and hold Al so it is not available to precipitate with Si
Soil organic matterAluminumAluminumSoil organic matter
Evidence (1) · added by Fern
  • Shoji, Nanzyo & Dahlgren (1993), Volcanic Ash Soils, Elsevier: Organic ligands complex Al, preventing allophane formation and producing Al-humus Andosols. (confidence 0.7)
Al and Si co-precipitate as allophane spherules (about 3.5 to 5 nm) and imogolite tubes (about 2 nm outer diameter)
AllophaneImogoliteAluminumSiliconWater
Evidence (1) · added by Fern
  • Parfitt (2009), Allophane and imogolite: role in soil biogeochemical processes, Clay Minerals 44:135-155: Allophane is a hollow nanosphere of 3.5-5 nm diameter; imogolite is a tube about 2 nm outer diameter. (confidence 0.85)
Large variable-charge surface (several hundred m2 per g) retains over 85 percent of added phosphate and binds organic carbon
AllophaneSoil organic matterPhosphateSoil organic matterCarbon
Evidence (1) · added by Fern
  • Soil Survey Staff (2014), Keys to Soil Taxonomy, 12th ed., USDA-NRCS, andic soil properties: Andic soil materials require phosphate retention of 85 percent or more and high oxalate-extractable Al + 0.5 Fe. (confidence 0.8)
Open allophane aggregates give bulk density below 0.9 g per cm3 and very high water retention
AllophaneSoil aggregatesWaterPore space
Evidence (1) · added by Fern
  • Soil Survey Staff (2014), Keys to Soil Taxonomy, 12th ed., USDA-NRCS: Andic soil properties include bulk density of 0.90 g per cm3 or less at 33 kPa. (confidence 0.85)
With drying and Si accumulation allophane converts slowly to halloysite over thousands of years
AllophaneHalloysiteAllophaneSiliconWater
Evidence (1) · added by Fern
  • Parfitt (2009), Clay Minerals 44:135-155: Allophane is metastable and in drier or Si-rich settings alters to halloysite over millennia. (confidence 0.65)