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Medieval demise of a Himalayan giant summit induced by mega-landslide

Abstract

Despite numerous studies on Himalayan erosion, it is not known how the very high Himalayan peaks erode. Although valley floors are efficiently eroded by glaciers, the intensity of periglacial processes, which erode the headwalls extending from glacial cirques to crest lines, seems to decrease sharply with altitude1,2. This contrast suggests that erosion is muted and much lower than regional rock uplift rates for the highest Himalayan peaks, raising questions about their long-term evolution3,4. Here we report geological evidence for a giant rockslide that occurred around 1190 ad in the Annapurna massif (central Nepal), involving a total rock volume of about 23 km3. This event collapsed a palaeo-summit, probably culminating above 8,000 m in altitude. Our data suggest that a mode of high-altitude erosion could be mega-rockslides, leading to the sudden reduction of ridge-crest elevation by several hundred metres and ultimately preventing the disproportionate growth of the Himalayan peaks. This erosion mode, associated with steep slopes and high relief, arises from a greater mechanical strength of the peak substratum, probably because of the presence of permafrost at high altitude. Giant rockslides also have implications for landscape evolution and natural hazards: the massive supply of finely crushed sediments can fill valleys more than 150 km farther downstream and overwhelm the sediment load in Himalayan rivers for a century or more.

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Fig. 1: Location maps of the Sabche breccia deposits.
Fig. 2: Chronological constraints on deposits related to the Sabche rockslide.
Fig. 3: Reconstruction of the Annapurna IV palaeo-summit before its collapse.
Fig. 4: Far-downstream signature of the reworked rockslide deposits evidenced by sediment carbonate content.
Fig. 5: Evolutionary sketch of the high peak emergence well above the ELA in a glaciated landscape undergoing sustained rock uplift.

Data availability

All data used in this study are from the published literature as referenced36,37,38 or presented in the Supplementary Information.

Code availability

To calculate minimal SF maps and reconstruct Annapurna IV palaeotopography, as shown in Extended Data Figs. 8 and 9, we wrote two original codes in MATLAB, described in Methods. The two codes are available from the corresponding author on reasonable request.

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Acknowledgements

J.L. thanks B. Sitaula for his invaluable logistic help in the field, L. Bollinger for his help during the helicopter flight in Sabche cirque and the numerous pictures he took and Y. Gunzburger, F. Carraro Braga, M. Manas and P. Kumar for initial discussions and modelling on the slope stability of the palaeo-summit. We also thank D. Burbank, S. Gallen and N. Hovius for their very positive and constructive reviews that greatly helped improve our manuscript. This study was funded by the ANR Calimero and the INSU-Syster and INSU-Artemis programmes. P.G.V. acknowledges funding from the French ANR-PIA programme (ANR-18-MPGA-0006). The Pleiades images were acquired in the framework of the Isis collaborative programme between the CNES and INSU. We thank the LMC14 (Laboratoire de Mesure du Carbone-14), ARTEMIS national facility (LSCE (CNRS-CEA-UVSQ)-IRD-IRSN-MC) for the 14C AMS results and the ASTER national facility (Cerege (CNRS, Aix-Marseille Université)) for the 36Cl AMS results.

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Authors and Affiliations

Authors

Contributions

J.L. designed the study, conducted the modelling and wrote the manuscript. J.L. and A.P.G. collected observations and samples. C.G. realized the digital terrain model, P.G.V. the IRSL measurements, V. Guillou and L.B. the 36Cl measurements, C.M., J.P.D. and V. Galy conducted the 14C measurements and T.R., C.F.-L., G.M. and J.L. handled the carbonate data and core drilling in the Ganga plain. P.G.V., C.F.-L. and V. Galy actively participated in the manuscript refinement.

Corresponding author

Correspondence to Jérôme Lavé.

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The authors declare no competing interests.

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Nature thanks Douglas Burbank, Sean Gallen and Niels Hovius for their contribution to the peer review of this work. Peer reviewer reports are available.

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Extended data figures and tables

Extended Data Fig. 1 Geologic map and cross-section of the Sabche cirque area.

Top, interpretative geologic map of the Sabche cirque area based on published maps28,71 west and north of the cirque. The TSS units that outcrop along those cliffs correspond to the base of the TSS series, namely, carbonate-rich sediments, Cambrian to Silurian in age and presenting an upward decreasing degree of metamorphism28. The different lithologic limits were extrapolated across the cirque based according to our observations made on photos taken from ultralight aeroplane and helicopter and from satellite images. Structures and bedding attitudes were also estimated from photos or from the tri-stereo digital elevation model. Bottom, interpretative structural cross-section AA′ (see location on main map) built according to published sections further west28,71 and to the bedding attitude we estimated from a large set of aeroplane photos or from the digital elevation model. The northern part of the section, which has been affected by the rockslide, is relatively well constrained because beddings are pretty well identifiable on photos. The southern part is much less constrained because the Sanctuary units show less identifiable beddings and because the structure is much more heckled with numerous small-scale folding. DD, Deolali Detachment; STD, South Tibetan Detachment.

Extended Data Fig. 2 Different facies of the breccia deposit in Sabche cirque.

Photos af taken from an ultralight aeroplane; see Supplementary Information Fig. SI-1-1). a, Compact, homogeneous, pulverized and indurated fine-grained breccia exposed over approximately 200-m-high cliffs. b,c Package of coarse and blocky material topped by more finely pulverized fine-grained breccia material. c,d Internal contacts between grey and yellowish breccia facies (issued from the Annapurna Yellow Limestone formation28) presenting inverted order and suggesting limited mixing during the rockslide collapse. d, Contact close to the southern base of the cirque deposit in its southern part: this contact, slightly sloping towards the north or northwest, presents as a thin band of shearing and microcrushing in which IRSL samples were taken (CA-273, CA-274 and CA-283). e, Rare preserved phantom of limestone dismantled strata, or jigsaw facies. f, In the southern part of the cirque, veneers of breccia deposit are preserved on the north-dipping flank of the cirque up to 4,350 m altitude (z2) and at the top of the eastern ridge of Machapuchare (Fig. 1) at about 4,570 m altitude (z1 is a satellite image taken on 30 December 2011). g, Saw-cut samples of compact and indurated facies exposed in the basal part of the deposit (CA-273, site of panel d): the breccia is made of finely crushed material with a few angular clasts.

Extended Data Fig. 3 Outcrops near Karuwa (site K in Fig. 1) exposing the stratigraphy of the granular avalanche breccia deposit.

a,b 40-m-high cliff overhanging the Seti river, exposing breccia of the granular avalanche material and cut by a small inset terrace capped by a filling of finely layered limestone-rich gravels of Pokhara conglomerates. c, Breccia facies with juxtaposition of parts made of limestone/marble of different colours with pockets of whitish elements and matrix within a set of darker elements and matrix. The size of elements, the proportion of clast versus matrix, as well as the carbonate content remain, however, similar between the different coloured areas. They are interpreted as a sign of incomplete mixing at the metre scale of the avalanche material issued from the basal Ordovician units that show alternating light and dark layers in the Sabche cirque along the steep southwest face of Annapurna IV (c′). d,e Internal part of the breccia showing dyke injection of a fluid-rich phase that coloured the breccia and the post-injection multiple brittle to ductile faulting and shearing of this dyke and of its shoulders. f, Schematic section of the contact between the avalanche brecciatic deposit and the gneissic bedrock of the Seti valley flanks. This contact shows a transition in terms of lithology and clast size: breccia with large (up to >1 m) and subangular to rounded boulders of local biotitic gneisses are progressively replaced by smaller angular elements (<30 cm) within a matrix-dominant material made of about 100% of TSS lithologies. The gneiss-rich unit, which corresponds to local material dragged and entrained at the base of the avalanche, contained quantities of millimetric to submetric pieces of vegetal debris (root, branch and trunk (g)) ripped from the sides of the valley and also whose density decreases rapidly away from the former valley wall. h,i Bedrock/breccia contact in the upper part of the thalweg showing a contact zone, 0 to 40 cm thick, made of a mixture of limestone breccia, local gneissic clasts and palaeosol pockets, including numerous wood debris, and the presence of a shearing zone of a few centimetres thickness. Green numerical codes correspond to the names of the samples (CA-XX-XX) dated by 14C.

Extended Data Fig. 4 Elements for reconstructing the volume of collapsed rockslide material in the Sabche cirque and the initial rockslide failure surface.

Maps of the base (a) and top (b) of the rock-avalanche brecciated deposits, including the interpolation constraints, and present-day residual thickness of the breccia deposits (c). d, Sabche rockslide scar identification from the transverse curvature (m−1) computed from the high-resolution (2-m pixel) topography. The recent scar surface (3 and 4) is characterized by step-like dihedrals that delineate planar faces with low curvature along the stratification/foliation planes and irregular faces following a set of fractures at 90°. By contrast, outside the scar (1 and 2), the topography shows the first marks of erosion and gullies organization towards a converging network.

Extended Data Fig. 5 The main dated relic of the rockslide deposit surface in the upper Sabche cirque.

a, Satellite image (Google Earth) of a large flat area in the northern part of the Sabche cirque. This flat area corresponds to the top of the rockslide deposit (4,600 m), which was amply resurfaced by glaciers except along its southern part, in which the original surface is covered with numerous multimetric blocks. b, Picture taken from an ultralight aeroplane of the area, south of which the multimetric blocks CA-13-260 to CA-13-265 were sampled. (A, original chaotic upper surface of the rockslide deposit; B, gently hilly surface of the hummocky moraine deposits; C, crested moraine left by the glacier issued from the southeastern face of Annapurna III and which is now deeply entrenched into the breccia deposit; D, recent moraine left by the glacier issued from the west face of Annapurna IV; E, present-day glacier issued from the west face of Annapurna IV.) c, Five of the six blocks sampled for cosmogenic 36Cl dating at the top of this relic surface. All the blocks of the surface consist of carbonate rocks: limestone, marly to sandstone limestone, sandstone marl. These lithologies are finely schistosed and their surface physically weathered.

Extended Data Fig. 6 Internal shear zone near the basal part of the rockslide deposit in the Sabche cirque and IRSL dating (see location in Fig. 1c).

a, The shear zone varies in thickness from a few centimetres up to 30 cm at the level of fish-like structures (to the left of the hammer). b, The shear zone (sample CA-13-283) appears as coloured bands of relatively compact breccia made of centimetre-sized angular clast within a finer yellowish matrix. c,d, Thin sections observed under a polarizing microscope, cut into the shear zone perpendicularly to the shearing plane and showing thin zones of homogeneous, finely fragmented almost glassy material within microbreccia facies with local remnants of larger clasts. e, Schematic sedimentologic description of the breccia around the shear zone at two sites, around 50 m apart (Extended Data Fig. 2d). f,g, Age distributions (fading-corrected) and kernel density estimate (KDE) plots for samples CA-13-283 and CA-13-273, respectively. IR50 ages and KDE are represented by filled circles and thick line, respectively. pIR225 ages and KDE are represented by open circles and dashed line, respectively.

Extended Data Fig. 7 Definition and validation testing of the hillslope SF exploration procedure in the Annapurna Range region.

a, Definition of the variables for the computation of the SF according to the 3D Hovland criterion67. b, Computation chart of the searching procedure of the ellipsoid-type failure surfaces that minimize the SF all over the topography of a given region. c, Validation test of the searching procedure in the case of a topographic step, 1 m high, dipping at 60° with φ = 15° and C = 0.116 Pa. The optimal ellipsoid surfaces at the four increments that present minimal SF are compared with close-formed solutions68,69. The SF values remain within 5% of those associated to these solutions whatever the nominal value (solid line) or that calculated with the 3D Hovland criterion applied to their geometry (dashed line) considered.

Extended Data Fig. 8 Results of the hillslope SF exploration in the Annapurna Range region.

a, Map of the minimum SF along the hillslopes of the Annapurna high relief found using the systematic searching procedure (Extended Data Fig. 7) within the area delineated by the dashed line. Calculation is made for an internal angle of friction of 35° and a cohesion, C, of 1.15 MPa. The steepest faces surrounding the highest peaks (black triangles), such as the south-southeast face of Annapurna I (A-I), one of the most challenging climbing routes in High Himalaya, present a SF lower than 1 and would be considered as unstable for this given cohesion value. Note that, for a given pixel, the search procedure may have found several optimal failures, of different sizes, whose centres of mass related to the same pixel: in this case, the failure with the minimum SF was chosen. A-II, Annapurna II; A-III, Annapurna III; A-IV, Annapurna IV; Ma, Machapuchare. b, Histograms of the values of the SF for different values of cohesion, C, between 0.5 and 2 MPa. For C = 2 MPa, almost all the hillslopes are apparently stable.

Extended Data Fig. 9 Palaeo-summit reconstruction.

a, Construction points used to build simplified topography of the palaeo-summit. This construction is essentially based on two main lines, whose geometry is explored in a random way: the palaeocrest (in cyan) and the palaeocliff southwest base (in blue). These lines are built as the sum of harmonics function (up to the eighth term) of random amplitude and phase. The two extremities of the palaeocrest have been chosen to prolong, on average, the direction of the present crest lines further west and east. Similarly, the extremities of the base of the southwest cliff and the isolated mobile point (in cyan) were chosen to prolong the southwest-facing cliffs of the Sabche cirque. Densifying points are then added before using the MATLAB interpolation function griddata. b, Map extent of the density (in log scale) of the random paths explored for the palaeocrest and the palaeobase, with one random example of path (solid black line). c, Same as b but for the elevation profile of the palaeocrest. In both graphs, purple lines indicate the 95% probability of the density of the a posteriori paths that respect both rockslide volume and hillslope stability constraints. d, Map and histogram (inset graph) of the SF values obtained through the searching procedure (Extended Data Fig. 7) applied, within dashed lines and for a cohesion value of C = 2 MPa, to one of the randomly generated palaeotopographies. e, Average shape of the topographies that satisfies rockslide volume and regional stability criterion, including a rose diagram of the optimal sliding direction N245° (that is, the direction that minimizes the SF on the failure surface). f, Histogram of the volumes of the collapsed summit explored by the generator of random topographies. 75% of the values fall within the range of the volume estimated for the rockslide. The topographies that satisfy the regional stability criterion are superimposed in pink colour. g, Histograms of the SF on the failure surface for cohesion values C = 2 MPa. The topographies that satisfy the rockslide volume are superimposed in a darker colour and those that satisfy both rock volume and regional stability criterion in pink colour.

Extended Data Fig. 10 Possible Sabche rockslide signature in the Gandak fan.

a, Stratigraphic log and carbonate content of two 50-m-long cores, GR1 and GR2, drilled in the Gandak fan72. The two boreholes GR1 and GR2 show relatively constant carbonate percentages close to the current river values (represented by the blue and grey lines, respectively). Nevertheless, GR2 is characterized by a 25–30% anomaly between −10 and −3 m and by a very strong 35–70% carbonate anomaly between −3 m and the surface. This anomaly was corroborated by further measurements on samples taken in a 3-m-deep small pit dug in close proximity to the GR2 drill site. Such a recent anomaly in carbonate content might correspond to deposition of the fine fraction of the sediments issued from the Sabche cirque erosion, 300 km further downstream. Whereas these carbonate-rich units are not directly dated, 14C ages in the GR1 core indicate that they are probably younger than about 1.5 kyr, which is compatible with a deposit related to the Annapurna IV collapse and more or less synchronous in the Pokhara conglomerate deposits. b, Residual topography obtained by subtracting a second-order polynomial fit (dashed lines denote Trend function in ArcGIS) to the topography (30 m SRTM) of the Narayani fan. This residual topography allows to highlight small topographic variations on the surface of the fan. It is seen that GR1 was drilled in the recent flood plain of the Narayani (in yellow to reddish colours), whereas GR2 was drilled in a north–south lobe 3 to 5 m higher than the rest of the fan (in bluish colours). This lobe, which was then re-incised on its eastern border by the Narayani (see zoomed-in image) could have been built during the episode of strong sediment input that followed the collapse in the Sabche cirque.

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Lavé, J., Guérin, C., Valla, P.G. et al. Medieval demise of a Himalayan giant summit induced by mega-landslide. Nature 619, 94–101 (2023). https://doi.org/10.1038/s41586-023-06040-5

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