Massive rock slope failures and episodic landform development generate complex Geohazards in the northwest Himalayan Syntaxis

Abstract

The Nanga Parbat-Haramosh massif (NPHM) forms the northern extension of the geotectonic region of the NW Himalayan syntaxis, with exceptionally rugged terrain, high relief, and steep rock walls the dominant landform. More than 130 large landslides have been identified in the NPHM involving massive rock slope failures and rock avalanches. Most terminated as crossvalley deposits in the river valleys and presently inhabited areas. Their interactions with other earth surface processes profoundly affect landform evolution. The example of the Batkor- Gilgit mega-slide illustrates the phenomena. The greatest concentration of landslides is in the Jalipur Section under Nanga Parbat, where overlapping rock avalanches and related valley fill provide the main sites of human settlement and modern infrastructure, and unusual exposure to geohazards. Landslide characteristics suggest a major role of seismic triggers, possibly rare mega-quakes. Adjustments to other processes in landslide- interrupted river valleys continue for millennia, and are a perennial influence on risks, notably debris flows. The geohazards involve complex interactions among different geomorphic process systems. .