Day 190Air 0 °CMeltwater 0 m³/sFront retreat 0 mLake depth at front 0 mSecchi 0 mCalvings 0FPS 0

Drag to orbit, wheel or pinch to zoom. Beige = coarse silt (settles within hundreds of metres), turquoise = fine glacial flour (stays suspended for days). The plume animates at about ten minutes per second; the calendar sets how much sediment enters.

Proglacial Lake

Why is the lake turquoise, and why does a glacier ending in deep water retreat so fast?

Time

Climate and ice

Sediment

Live readouts

Terminus position and lake clarity

Meltwater and Secchi depth

Experiments

Each button runs ten model years headless and lists the result.

Independent numerical checks

Controls and missions

Drag / one finger: orbit; wheel / pinch: zoom; three camera presets.
Missions: (1) keep the August Secchi depth above 3 m; (2) find the coarse-silt size whose plume just reaches the outlet; (3) compare retreat for the calving constant 0.5 and 2; (4) get a decade with less than 100 m of retreat.

The science

Meltwater. Degree-day melt, M = DDF · max(T, 0), DDF = 7 mm w.e. K⁻¹ d⁻¹ [перевірити за джерелом], over a 14 km² glacier: Q_in = M · A_g, plus a 0.4 m³ s⁻¹ base flow. Air temperature is a synthetic cycle (mean 0.5 °C, amplitude 9.5 K) plus your warming.

Calving and flotation. The thickness at which ice floats is H_f = (ρ_w/ρ_i) h_w ≈ 1.09 h_w. The calving speed follows a Brown-type law, u_c = k h_w with k = 0.7 yr⁻¹ (model value for a lake; tidewater glaciers are faster [перевірити за джерелом]), multiplied by up to 3 when the front is within 1.5 H_f. The terminus moves by dx/dt = u_i − u_c − (M − M_ref)/α with ice speed u_i = 80 m yr⁻¹ and surface slope α = 0.05. The bed is over-deepened just behind the front, so a retreat can run away (calving instability).

Lake level. A_L dh/dt = Q_in − Q_out + V_calved·ρ_i/ρ_w with a broad-crested weir Q_out = 1.7 b h^3/2, b = 45 m, A_L = 3.5 km².

Sediment. Stokes settling, w_s = (ρ_s − ρ_w) g d² / (18 μ), μ = 1.5 mPa s (cold water), ρ_s = 2650 kg m⁻³. Fine flour (4 µm) falls 1 m in about 1.2 days, coarse silt (40 µm) in about 17 minutes. Lake-wide boxes: V dC/dt = Q_in C_in − Q_out C − A_L w_s C. The picture shows a 96 × 48 upwind advection-diffusion-settling grid in a 3 m surface layer with a prescribed, divergence-free flow (not a hydrodynamic model). Secchi depth ≈ 1.7 / k with extinction k = 0.1 + 35 C (C in kg m⁻³) [model value].

Simplifications. One lake box, no thermal stratification, no subglacial hydrology, constant ice speed, prescribed plume flow, synthetic temperatures. All coefficients are illustrative model values, not a calibrated reconstruction of any real lake. Assets built with Blender; scene by Three.js.