Add water physics, river currents, volcanic system with lava & new land

Groundwater aquifer (valley springs):
- Per-region subsurface water table recharges from rainfall + lateral seepage
  from uphill neighbours; valley floors (≥2 higher neighbours) develop springs
- GROUND_SPRING_EMERGES places a permanent water source block at the lowest
  natural terrain point; vanilla fluid physics carries it downhill from there
- Active springs feed riverFlowIntensity for erosion even without rain

River current physics (real player forces):
- Every 4 ticks, players in flowing water receive a velocity push via
  FluidState.getFlow() — the exact direction Minecraft's own rendering uses
- Force scales with fluid level: level 7 (near source) = strong; level 1 = gentle

Hydraulic erosion:
- HYDRAULIC_EROSION fires whenever flow intensity is significant, rain-independent
- Flowing water adjacent to stone/gravel/sand/dirt progressively softens it:
  stone→gravel→sand→air; river valleys widen over time

Volcano lifecycle (DORMANT→BUILDING→ERUPTING→COOLING→FERTILE→DORMANT):
- High-elevation regions (avg surface Y ≥ 85) registered as potentially volcanic
- LAVA_FLOW places source blocks at summit; vanilla physics flows them downhill
- ASH_DEPOSIT covers surrounding terrain with tuff/gravel; kills surface plants;
  ash clouds spread to adjacent regions with air pollution spike
- COBBLESTONE_FORMS solidifies lava: lava+water→cobblestone, lava+air→basalt
  — creates permanent new terrain that did not exist before the eruption
- FERTILE phase: soil fertility +30, contamination −20, rapid pollution decay
- Volcanic ambience: fire crackling during eruption, deep rumble while building

New commands: /lw events (active climate events), /lw volcanoes (lifecycle states)
New ClimateEventType: VOLCANIC_ERUPTION
New WorldEffectTypes: GROUND_SPRING_EMERGES, HYDRAULIC_EROSION, LAVA_FLOW,
  ASH_DEPOSIT, COBBLESTONE_FORMS

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -53,6 +53,11 @@ All effects are real block changes players can see:
 | Wildfire | Drought > 70, thunder > 0.5 | Fire placed on surface vegetation |
 | Water pools form | Rain + barren/sparse terrain | Water source blocks in surface depressions |
 | **River carve** | High accumulated water runoff | Water channels carved through natural terrain; gradually deepens |
+| **Ground spring** | Saturated aquifer in valley floor | Permanent water source placed; river flows downhill naturally |
+| **Hydraulic erosion** | Flowing water adjacent to rock | Stone → gravel → sand → air; valley walls slowly widen |
+| **Lava flow** | Volcanic eruption | Lava source blocks placed at summit; flows and reshapes terrain |
+| **Ash deposit** | Active eruption or nearby blast | Grass → tuff, soil → gravel; surface plants killed over wide area |
+| **Cobblestone forms** | Lava cooling | Lava + water → cobblestone; lava in air → basalt; new permanent land |
 | Pollution particles | Pollution > 10 | Smoke particles in degraded regions |
 
 ### Player Feedback — **Complete**
@@ -126,13 +131,48 @@ Automatically triggered when regional conditions reach critical thresholds. All
 - Visible in the compass HUD next to the region coordinates
 - Full trend detail in `/lw atmosphere`
 
-### River Erosion — **Complete**
+### Groundwater & Springs — **Complete**
+
+- Every region tracks a subsurface aquifer level that recharges slowly from rainfall
+- Underground seepage: high-elevation neighbours drain laterally into the aquifer of lower regions (water flows underground even between sim cycles)
+- When the aquifer is saturated in a **valley floor** (≥2 higher neighbours), a `GROUND_SPRING_EMERGES` effect fires — a water source block is placed at the lowest natural terrain point
+- The spring flows downhill under Minecraft's own fluid physics, forming a permanent river without further simulation involvement
+- Active springs contribute to river erosion intensity even without rain
+
+### River Erosion & Hydraulic Erosion — **Complete**
 
 - Accumulated water runoff intensity tracked per region (flow from higher → lower elevation)
 - When flow intensity crosses the threshold (80 units), a `RIVER_CARVE` world effect fires
-- Block effect: water source placed on natural terrain (sand/dirt/gravel/grass); at high intensity the block below is also removed, deepening the channel
+- Block effect: water source placed on natural terrain; at high intensity the block below is removed (deepening channel)
+- **Hydraulic erosion** fires independently of rainfall whenever significant flow intensity is present: flowing water (level 1–7) adjacent to soft rock softens it — stone → gravel → sand → air — progressively widening river valleys
 - Rivers form gradually over many sim cycles — permanent terrain changes
 
+### River Current Physics — **Complete** (real player forces)
+
+- Every 4 ticks, all players standing in **flowing** water (level 1–7) receive a directional velocity push
+- Force direction: `FluidState.getFlow()` — the exact vector Minecraft already computes for its own flow rendering; currents always point the same way the water visually flows
+- Force magnitude: scales with flow level — level 7 (one block from a spring, fastest) pushes hard; level 1 (distant, slow lowland river) barely nudges
+- Mountain rivers are genuinely dangerous to wade against; lowland rivers are gentle enough to cross
+- Boats are naturally carried by vanilla water physics; swimming players and mobs now feel the additional push
+
+### Volcanic System — **Complete** (new land formation)
+
+Four-phase lifecycle per high-elevation region (average surface Y ≥ 85):
+
+| Phase | What Happens |
+|-------|-------------|
+| **DORMANT** | Normal state; rare stochastic chance to awaken (~0.2% per check) |
+| **BUILDING** | Seismic venting — mild pollution spike; player broadcast warns of imminent eruption |
+| **ERUPTING** | `LAVA_FLOW` places source blocks at the summit; `ASH_DEPOSIT` covers surrounding terrain; ash clouds spread to adjacent regions; vegetation dies in the eruption zone; air pollution spikes; lasts ~40 sim cycles |
+| **COOLING** | `COBBLESTONE_FORMS` converts lava adjacent to water → cobblestone; lava in air → basalt; permanent new terrain created where none existed before |
+| **FERTILE** | Volcanic minerals boost soil fertility +30, contamination −20; pollution decays rapidly; succession cap can rise; then returns DORMANT |
+
+Visible effects:
+- Lava flows downhill under vanilla physics, permanently reshaping terrain
+- Ash converts grass → tuff, loose soil → gravel; kills surface plants across a wide area
+- New cobblestone and basalt islands form where lava met water
+- Players in active eruption zones hear fire crackle ambience; building-phase rumble in BUILDING regions
+
 ### Tidal Simulation — **Complete** (physical blocks)
 
 - Two tidal cycles per Minecraft day (24 000 ticks) using a sine wave
@@ -210,6 +250,8 @@ All commands require permission level 2.
 | `/lw simulate <ticks>` | Force N simulation cycles on all active regions |
 | `/lw stats` | Simulation profiler statistics |
 | `/lw modules list` | List all registered modules and their enabled state |
+| `/lw events` | List all active climate events (drought/wildfire/flood/eruption) with epicentre, severity, affected regions |
+| `/lw volcanoes` | List all tracked volcanic regions and their current lifecycle phase |
 | `/lw demo degrade` | One-command demo: degrade current region to barren |
 | `/lw demo recover` | One-command demo: restore current region to mature forest |
 
@@ -291,13 +333,16 @@ LivingWorldMod (NeoForge event wiring)
             applySeasonalEffects()          [soil/water/veg seasonal]
             applyClimateWarmingEffects()    [drought pressure from CO₂]
             applyWaterRunoff()              [elevation-based; river erosion]
+            applyGroundwaterAndSprings()    [aquifer recharge; valley springs]
             applyDynamicCapUpdate()         [raise/lower succession ceiling]
             applySeedDispersal()            [corridor-boosted recolonisation]
             recordHealthTrend()             [↑↓→ trend tracking]
             applyClimateEvents()            [drought/wildfire/flood events]
+            applyVolcanicActivity()         [volcano lifecycle; lava/ash/new land]
 
 LivingWorldMod platform hooks:
     updateTidalEffects()                    [block-level tidal simulation]
+    applyRiverCurrents()                    [player/entity velocity in flowing water]
     initializeRegionFromBiome()             [biome-aware starting values]
     checkPlayerRegions()                    [HUD, effects, ambient sounds]
     scanAndRecordFurnaceActivity()          [pollution from lit furnaces]
@@ -320,7 +365,8 @@ Requires NeoForge 21.1.172 / Minecraft 1.21.1.
 ## Planned / In Progress
 
 - Full worldgen integration (custom biome distribution, terrain shaping beyond post-load modification)
-- `/lw events` command to list active climate events and their affected regions
-- Persistence for river flow intensity and accumulated seed rain across restarts
+- Persistence for river flow intensity, groundwater level, and volcanic state across restarts
 - Multiplayer region ownership / notification system
-- More succession stages (wetland, alpine, volcanic)
+- More succession stages (wetland, alpine, volcanic basalt plain)
+- Snowmelt rivers: winter snow accumulation releases as meltwater in spring
+- Player damage in active eruption zones (lava proximity heat)