The Canterbury Earthquake Sequence (CES) altered the morphology of the Avon-Heathcote Estuary. Much of the tidal lagoon uplifted by 0-0.4m, reducing the tidal prism by ~12%-18%. The abrupt CES changes follow a theorized 400-year period of gradual subsidence and tidal prism increase. Questions remain regarding whether estuary morphology has reached a post-quake equilibrium. Inlet-area relationships would suggest a reduction in inlet cross-sectional area as a possible response. The question of whether the estuary will tend to infill or erode has great relevance to the surrounding suburbs' resilience to sea level rise.