Potential Natural Hazards in Kathmandu, Nepal: Lessons from Stratigraphic Analysis of the Pleistocene Succession in the Kathmandu Valley

Abstract

The Kathmandu Valley is an intermontane piggyback basin filled with more than 550 m of fluvio-lacustrine deposits overlying irregular bedrock. Over the past two decades, rapid and largely unregulated urban expansion has heightened concerns about geohazards. Stratigraphic and chronological studies conducted over the past 25 years indicate that the basin once hosted an extensive paleolake represented by the Gokarna, Thimi, and Patan Formations, which were deposited during successive lake-level rises between ca. 50 ka and 10 ka.
The Pleistocene succession records several large-scale natural hazards, including subaqueous landslides and associated tsunamis, soft-sediment deformation involving mud softening and fluidization, mud volcanism, widespread lateral spreading, and liquefaction reaching depths of up to 5 m. The most extensive event involved kilometer-scale lateral spreading across the delta plain, most likely triggered by a major paleoearthquake.
These findings demonstrate that the Kathmandu Valley has repeatedly undergone catastrophic deformation of its unconsolidated lacustrine sediments during past seismic events. Because thick, soft muds of the Gokarna Formation still occur widely at shallow depths, similar large-scale ground deformation may recur during future earthquakes. Comprehensive geotechnical studies and stricter control of urban development are urgently needed to mitigate seismic risks in this rapidly expanding basin.