The Kula Plate is an ancient tectonic plate that used to subduct under Alaska. That is the reason why oceanic plates always subduct under another plate. At Taitao, the Chile Triple Junction and the Nazca Plate subduct the South American Plate. The plate does not subduct smoothly and can become 'locked' with the North American plate. The side that begins to subduct earlier enters the eclogitization level earlier. In such cases, it is more difficult to subduct water through the thermohaline circulation.