Presets
Playback
Glacier and fjord
Thickness of the ice at the front, the water depth in front of it and how fast it flows.
Crevasses and calving
Stretching rate of the ice, how quickly it dies away inland, meltwater in crevasses and the size of detached blocks.
Layers
Model checks
The science
Flotation and freeboard
Ice is lighter than sea water (rho_i = 917, rho_w = 1028 kg/m3). A glacier of thickness H floats once H < H_f = rho_w d / rho_i, where d is the water depth. A floating slab sticks out of the water by H (1 - rho_i / rho_w); a grounded front sticks out by H - d. The height above buoyancy is H - H_f: near zero means the front is close to floating and easy to calve.
Crevasse depth (Nye / Benn)
Glen's flow law strain_rate = A (stress)^3 gives the tensile stress in stretching ice, R_xx = 2 (strain_rate / A)^(1/3). A dry surface crevasse opens down to R_xx / (rho_i g), and water of depth d_w in it pushes it deeper by (rho_fw / rho_i) d_w. Calving is assumed when this depth reaches sea level, i.e. equals the freeboard. Solving for the strain rate gives the critical value shown in the readouts.
Calving cycle
The strain rate dies away inland as exp(-x / L), so the crevasse forms where it first exceeds the critical value, at x_c = L ln(strain_rate / critical) behind the front. In this model the front advances at speed u and a block of length m x_c detaches each time it has advanced by x_c. With m = 1 the front cycles around a fixed place (calving flux equals ice flux); with m > 1 it retreats; thinning (smaller H) lowers the freeboard and pushes the system towards calving.
Honest simplifications
Real calving also involves basal crevasses, melt undercutting at the waterline, tides, ice-mélange back-pressure and block rotation; those are folded into the single size ratio m. Hydrostatic forces use the textbook 1/2 rho g h^2 per metre of width. Glen's law uses a temperate-ice rate factor A = 2.4e-24 per Pa^3 per second. The animation runs about 10 times faster than real time for readability: 1 s is about 0.1 year.
What to try
- Pick Land-terminating: the water is shallow, the freeboard is huge and no crevasse can reach it, so the front only advances.
- Raise the strain rate slowly until Calving? turns to yes, exactly at the critical value on the first graph.
- Add meltwater to the crevasse: it deepens the crack and lowers the critical strain rate.
- Pick Large buoyant bergs, or turn on thinning, and watch the front position graph drift backward.