St Cross alumnus contributes to major study of Alaskan megatsunami

St Cross alumnus Dr Thomas Monahan (2022, DPhil Engineering Science) has contributed to a major international study of one of the largest tsunamis ever recorded, offering new insight into the increasingly complex natural hazards emerging in a warming Arctic.

Dr Monahan, now the W.W. Spooner Junior Research Fellow at New College and a Senior Research Associate in Oxford’s Department of Engineering Science, completed his DPhil in Engineering Science in 2025. His research sits at the intersection of oceanography, engineering, and scientific machine learning. During his time at St Cross, Thomas was awarded a Community Bursary in recognition of his entrepreneurial work as founder of Tidal Prophet, through which he has sought to translate advances in ocean forecasting into practical tools for environmental and industrial use.

The study, published in Science, examines the megatsunami that occurred in Tracy Arm fjord, southeast Alaska, on 10 August 2025. The wave was triggered when more than 60 million cubic metres of rock collapsed into the fjord following rapid glacial retreat. The resulting tsunami reached a run-up height of 481 metres, making it the second-highest tsunami ever recorded.

Dr Monahan helped analyse the unusual long-lived waves that followed the initial tsunami. After the landslide, water continued to oscillate within the steep-sided fjord for more than a day, producing seismic signals that were detected globally. Using seismic observations, numerical modelling, and data from the new Surface Water and Ocean Topography satellite, the research team was able to study these standing waves in unprecedented detail.

The work builds on Dr Monahan’s earlier research identifying a similar event in East Greenland. In the Tracy Arm study, the researchers coined the term “landslide-induced seiche” to describe this phenomenon, in which a landslide-generated wave becomes trapped within an enclosed basin and continues to reverberate.

The findings have important implications for the monitoring of remote glaciated regions. The landslide occurred with little warning, and satellite imagery did not show clear slope movement before the collapse, although small seismic signals were detected in the days beforehand. As climate change accelerates glacial retreat and destabilises Arctic landscapes, such events are expected to become an increasing concern.