This research article, published in the Proceedings of the National Academy of Sciences, uses satellite radar data to document the intrusion of warm seawater beneath the grounded ice of Thwaites Glacier in West Antarctica. The study reveals that the boundary between grounded ice and floating ice is not a fixed line but rather a “grounding zone” that can extend several kilometers. This zone is influenced by tidal cycles, causing seawater to intrude under the glacier at high tide, leading to accelerated melting of the grounded ice. The research suggests that this process may be a key factor in the rapid retreat of the glacier, which is a major contributor to sea level rise. The study also highlights the importance of understanding subglacial hydrology in predicting future glacier retreat.