Geomorphologic and Hydrogeologic Characteristics of Populated Rockslide Deposits (Sagarmatha National Park, Khumbu Himal, Nepal)

Abstract

Surface morphology and internal composition of large rockslide deposits have been frequently studied, but their hydrogeologic conditions and consequences for (drinking) water quality and quantity on such deposits are largely unknown. In this study we provide first information on this critical relationship for two large rockslide deposits in the Khumbu Himal (Nepal), which are at the same time the main settlement areas in the region. In the first step, we investigated the Lukla and the Namche-Khumjung rockslides with respect to their dimensions and internal composition based on orthophotos and digital elevation models, geomorphologic field mapping, and the analysis of rockslide outcrops. Secondly, we studied their hydrogeologic characteristics by means of spring water mapping, sampling and analyses. As a consequence of the fragmented and highly shattered rockslide material, both deposits are characterized by 1) effective infiltration, 2) short residence times of percolating water and 3) by only small amounts of available spring water and surface runoff at all. Human activity on the studied rockslide deposits can therefore be described as an ambivalent relationship: On the one hand, the rockslide deposits provide a gentle topography and the only available areas for extensive settlements and agriculture in the steep upper DudhKosi catchment; On the other hand, their internal composition accounts for water scarcity-a critical issue for the local population demanding for adaptation strategies, especially in the light of the ever-increasing trekking and expedition tourism in the region.

Geomorphic Processes, Rock Quality and Solid Waste Management—Examples from the Mt. Everest Region of Nepal

“…As a consequence of the devastating earthquakes in April and May 2015, the Lukla and Khumjung rockslide deposit might be particularly prone to landslides and debris flows [42] [43]. It is highly possible that the stability of the shattered material is even further reduced and that its internal composition as well as its internal watercourses has been altered.…”

Landslides and other damage to buildings and infrastructures following the April–May 2015 earthquake sequence, Solukhumbu District, Eastern Nepal

“…2). Gorge sections (quartzites, paragneisses) alternate with wider sections, often corresponding to very large rockslide deposits, as observed at Namche-Khumjung, and between Phakding and Lukla (Heuberger 1986;Weidinger et al, 2014;Goetz et al, 2015) and close to Kharikhola settlement (Fort et al, 2017). A few relicts of glaciations (morainic deposits) exist, as suggested by earlier work (Heuberger and Weingartner, 1985;Owen et al, 2000;Fort 2004).…”

“…However, massive heterogeneous rockslide deposits, still undated, produced upstream river valley damming, hence controlling the nature of valley fills, such as lacustrine deposits (Ghat) and associated prograding gravel deposits (Chuserma). All these late Quaternary formations were later dissected, hence forming stepped gravelly sandy river terraces and debris fans (Goetz et al, 2015;Posch et al, 2015). Such large mass wasting material and its related deposits are estimated to represent volumes of >10 8 m 3 covering an area of c. 5.5 km 2 (Goetz et al, 2015), with a particularly marked thickness (>150-300 m) close to Ghat and Cheplung (Fig.…”

A Perspective of the Cumulative Risks from Climate Change on Mt. Everest: Findings from the 2019 Expedition

“…There is a diversity of landslide scarps and deposits, and the village of Namche Bazar (below Mt. Everest) was built in the bowl-shaped scarp from a past landslide [ 13 ]. That scarp cuts into an earlier massive rockslide--the Khumjung slide, which is currently the sixth-largest rockslide documented in Nepal [ 12 ].…”

“…This massive rockslide resulted from a 2.1 × 109 m 3 volume of rock material sliding southward off the Khumbila peak, where remnants make up the small E–W-trending ridge that separates Khumjung and Kunde from Namche [ 4 ]. Rockslides of this magnitude are thought to account for a large percentage of the erosion across the high-relief Himalaya [ 13 , 14 ]. High-magnitude slides occur infrequently and may be triggered by earthquake events [ 14 , 15 ], where rock strength plays a role in the frequency of occurrence.…”