Hydrate-bearing sediment
Free gas / dissociation cap
Migrating gas bubbles
GHSZ base (phase boundary)
Failed / sliding column
This cross-section walks down a real submarine slope one column at a time, solving the hydrate phase-equilibrium boundary independently at each point as water depth increases with distance down-slope — so the gas hydrate stability zone (GHSZ) genuinely thins and deepens across the profile rather than existing at a single point. Where hydrate dissociates fastest, the resulting excess pore pressure doesn't just sit locally: it obeys a real 1D diffusion equation that spreads it into neighbouring columns before it drains away, then each column's own infinite-slope factor of safety responds to its local depth and local pore pressure. Push enough columns below a factor of safety of 1 and the failure becomes retrogressive — a failed column dumps its load on the next one down-slope, letting one weak patch drag its downhill neighbours into a spreading slide, the mechanism proposed for hydrate-linked submarine landslides such as Storegga.