Subsidence and sedimentation dynamics of the lakeside part of the Rita River delta in the rupture zone, the northwestern coast of Lake Baikal

Abstract

Delta subsidence is one of the key problems of human life as these areas are developed quite fast. The process is natural and depends on many factors, the influence of which has not yet been sufficiently studied. This study is aimed to identify changes in the earth’s surface of the lakeside part of the Rita River delta on the northwestern coast of Lake Baikal, where a zone of seismically induced gravitational ruptures were recently mapped. To assess topographic changes, we used the calculation of the difference in multi-temporal digital surface models (DSM) obtained in two local areas from ultra-high resolution unmanned aerial photography in 2020 and 2021. We established that the subsidence of the lakeside part of the delta occurred on average by 5–10 cm over 11 months and 19 days. These values are associated with natural sediment compaction. In places of their accumulation, aggradation occurs by similar values, compensating the balance of deposits. In the seismically induced gravitational failures in the absence of alluvium, subsidence reached 33–37 cm, which indicates active endogenous and exogenous processes in the Kocherikovsky fault zone. The largest negative and positive vertical topographic changes up to 40 cm occurred within the beach and were associated with wave-cutting activity. The most extreme swampy part of Cape Rytyi experienced the maximum subsidence per a year. The greatest accumulation of alluvium occurred in the southern section of the Rita River delta in a settling expressed in the surface and coinciding with the zone of recent ruptures, as well as in an accumulative flow that overlaps the zone of surface deformations. With the exception of this part, discontinuities are well exhibited on DSM that means they continue to develop despite intensive sedimentation. Comparison of multi-temporal DSM and DTM by calculating the difference in elevation for each node (pixel) of the model is a promising and inexpensive method for monitoring surface deformations.