Skip to content

Erosion — Thermal vs Hydraulic

Hesiod ships two families of erosion. Reach for them after you have a base heightmap (see Getting Started).

A raw NoiseFbm heightmap before any erosion: soft, rounded lumps with no drainage structure. The base terrain these recipes start from. Source graph: erosion-before.hsd.

Thermal erosion

Material slumps downhill once a slope exceeds the angle of repose (talus angle): peaks soften, debris collects as scree at the base. Use it to make raw noise read as weathered rock.

  • Thermal — the workhorse; smooths slopes past a talus threshold.
  • ThermalScree — accumulates scree/talus at slope bases.
  • ThermalFlatten — flattens toward stable plateaus.
  • ValleyFill, DepressionFilling, DepositionFillHoles — deposition-side cleanup (fill pits and basins).

The base terrain after Thermal erosion: peaks are softened and debris has gathered as scree at the slope bases. NoiseFbm → Thermal. Source graph: erosion-thermal.hsd.

Hydraulic erosion

Simulated water flows downhill, picking up and depositing sediment: it carves drainage channels and river valleys and lays down alluvial deposits.

  • HydraulicParticle — the workhorse; particle-based water erosion.
  • HydraulicStreamLog — stream-power channel carving.
  • HydraulicSaleve, HydraulicProcedural — alternative hydraulic models.
  • Rifts — incised rift/channel features.

The same base terrain after HydraulicParticle erosion: water has carved dendritic drainage channels and valleys. NoiseFbm → HydraulicParticle. Source graph: erosion-hydraulic.hsd.

Choosing and combining

A common recipe is thermal first, then hydraulic: thermal settles slopes to a believable repose angle, then hydraulic carves drainage into that surface. Most erosion nodes accept a mask input so you can confine erosion to chosen areas — see Masks & Selectors (e.g. erode only steep slopes with SelectSlope).

  • Stratify — Strata, StrataCells, StrataPlates, StrataTerrace (sedimentary banding/terracing).
  • Coastal — CoastalErosionDiffusion, CoastalErosionProfile (shoreline erosion).

See also