Kenneth Hewitt

The Karakoram Anomaly? Glacier Expansion and the ‘Elevation Effect,’ Karakoram Himalaya

Abstract In the late 1990s widespread evidence of glacier expansion was found in the central Karakoram, in contrast to a worldwide decline of mountain glaciers. The expansions were almost exclusively in glacier basins from the highest parts of the range and developed quickly after decades of decline. Exceptional numbers of glacier surges were also reported. Unfortunately, there has been no on-going measurement of climatic or glaciological variables at these elevations. The present article examines possible explanations for this seemingly anomalous behavior, using evidence from short-term monitoring programs, low-altitude weather stations, and the distinctive environmental characteristics of the region. The latter involve interactions between regional air mass climatology, its seasonality, topoclimate or ‘verticality’ effects on glaciers with extreme altitudinal range, climatic sensitivities of heavy versus thin supraglacial debris, and complex temperature distributions in ice masses with ice falls throughout critical elevations. Valley climate stations indicate increases in precipitation over the past 50 years and small declines in summer temperatures, which may indicate positive trends in glacier mass balance. However, the suddenness of the expansions is problematic, as is their confinement to glaciers from the highest watersheds while others continue to retreat. Thermal shifts in ice masses with extreme altitude ranges may be even more critical, leading to an accelerated redistribution of ice mass by elevation.

Reframing disaster policy: the global evolution of vulnerable communities

The Social Construction of Disaster Disaster is widely perceived as an event beyond human control. The capricious hand of fate has moved against unsuspecting human communities, creating massive destruction and despair.[i] The sudden randomness of the event accentuates the cruelty of its effects, as surely the victims would have acted differently, had they known the risk. Other nations and organizations rush humanitarian aid to rebuild damaged communities, but stop short of examining the policies and practices that contributed to the event.

Catastrophic landslides and their effects on the Upper Indus streams, Karakoram Himalaya, northern Pakistan

Abstract The paper examines the nature and geomorphic influences of deposits from rock avalanches that obstruct rivers. Most of the 115 rockslide–rock avalanche events identified in the Karakoram Himalaya straddled one or more stream valleys. At least 73 of these landslides formerly dammed the Indus or its tributaries. Upstream of the barriers, remnants exist of once very extensive lacustrine deposits. The stability and long-term survival of dams from large rock avalanches is addressed, and the reasons for the gradual or phased, rather than catastrophic and sudden, breaching. Case histories emphasise the erosional and depositional forms associated with the barriers. They are reconstructed in terms of the emplacement and properties of the deposits from rock avalanches, and the response of the river to interruption by them. These barriers have exerted a substantial control over stream response and development for most of the Holocene at least. Today, they are associated with distinctive features of channel form and thalweg, river terrace systems, intermontane sediment sinks and sources, and local erosional forms in bedrock. More broadly, the landslide barriers have created a naturally fragmented river system. Deposition and erosion in the lower few tens or hundreds of meters of the Upper Indus stream valleys have been dominated by epicycles of aggradation, trenching, and downcutting that mainly reflect the scale, timing and history of each barrier. The landforms involved are only indirectly related to the late-glacial and paraglacial conditions that have, hitherto, been regarded as the main explanation.

Glacier Change, Concentration, and Elevation Effects in the Karakoram Himalaya, Upper Indus Basin

Abstract This paper seeks to explain evidence of distinctive late- and post-Little Ice Age glacier change in the Karakoram Himalaya and a recent, seemingly anomalous, expansion. Attention is directed to processes that support and concentrate glacier mass, including an all-year accumulation regime, avalanche nourishment, and effects related to elevation. Glacier basins have exceptional elevation ranges, and rockwalls make up the larger part of their area. However, more than 80% of the ice cover is concentrated between 4000 and 5500 m elevation. Classification into Turkestan-, Mustagh-, and Alpine-type glaciers is revisited to help identify controls over mass balance. Estimates of changes based on snowlines, equilibrium line altitudes, and accumulation area ratio are shown to be problematic. Extensive debris covers in ablation zone areas protect glacier tongues. They are relatively insensitive to climate change, and their importance for water supply has been exaggerated compared to clean and thinly covered ablation zone ice. Recent changes include shifts in seasonal temperatures, snowfall, and snow cover at high elevations. Understanding their significance involves rarely investigated conditions at higher elevations that lack monitoring programs.

Tributary glacier surges : an exceptional concentration at Panmah Glacier, Karakoram Himalaya

Four tributaries of Panmah Glacier have surged in less than a decade, three in quick succession between 2001 and 2005. Since 1985, 13 surges have been recorded in the Karakoram Himalaya, more than in any comparable period since the 1850s. Ten were tributary surges. In these ten a full run-out of surge ice is prevented, but extended post-surge episodes affect the tributary and main glacier. The sudden concentration of events at Panmah Glacier is without precedent and at odds with known surge intervals for the glaciers. Interpretations must consider the response of thermally complex glaciers, at exceptionally high altitudes and of high relief, to changes in a distinctive regional climate. It is suggested that high-altitude warming affecting snow and glacier thermal regimes, or bringing intense, short-term melting episodes, may be more significant than mass-balance change.

Catastrophic Landslide Deposits in the Karakoram Himalaya

In July 1986, three catastrophic landslides deposited about 20 x 106 cubic meters of debris on Bualtar Glacier in the Karakoram Himalaya. A sudden acceleration and superficial breakup of the glacier provided an opportunity to examine the fresh deposits in depth. Beneath a surface layer of large boulders, finer materials, mainly sand and silt, made up half of the total volume. The fine materials were formed during the rock avalanche from mostly intact, massive rock of the source zone. Velocity estimates suggest that this disaggregation occurred in less than 2 minutes. Coarse materials remained in bands of uniform lithology, but the fine materials had diffused throughout the landslides. A small amount of carbonate appears to have been calcined by frictional heating, presumably at the base of the initial sliding masses. These observations are relevant to understanding the mechanisms of catastrophic landslides. Other nearby rock avalanche deposits indicate that landslides are an important geomorphic process in the area and that they pose a continuing risk to human activity.

Karakoram glacier surge dynamics

Quincey, D. J., Braun, M. Glasser, N. F., Bishop, M. P., Hewitt, K., Luckman, A. (2011). Geophysical Research Letters, 38, Article Number: L18504.

Disturbance regime landscapes: mountain drainage systems interrupted by large rockslides:

The paper examines the role of rockslide-rock avalanches in mountain landscapes, and the landforms associated with them. While the landslides are extremely short-lived events, rock wall detachment scars and rock avalanche deposits can persist for long periods as influences on landscape development. Especially significant are rock avalanches with complex runout and emplacement related to interactions with rugged terrain or deformable substrates. Their characteristics greatly increase the scope of landscape disturbance. Hundreds of rock avalanches are now known, worldwide, that have formed crossvalley barriers interrupting mountain drainage systems. Many have done so for millennia or tens of millennia. They give rise to distinctive sediment assemblages, constructional and erosion landforms generated by other processes responding to the landslides and constrained by them. A landslide interruption epicycle of five phases is described, and related sediment assemblages. These provide the basis for defining a landslide interrupted valley landsystem. Its full significance is seen in mountain drainage basins affected by multiple landslide interruptions. These create naturally fragmented fluvial systems, in which a disturbance regime geomorphology is identified. Stream profiles, sediment delivery, and related landforms are kept in a chronic state of disequilibrium with respect to climatic and geotectonic controls, and drainage organization. The transHimalayan Upper Indus Basin provides an example, a large high mountain drainage system fragmented by more than 170 late Quaternary rock avalanches. In this case, as elsewhere, misidentification of rock avalanches led to neglect of their role in Quaternary histories. The nature and limitations of disturbance regime geomorphology are discussed, and broader implications for mountain landscapes.

Glacier and landslide feedbacks to topographic relief in the Himalayan syntaxes

Despite longstanding research on the age and formation of the Tibetan Plateau, the controls on the erosional decay of its margins remain controversial. Pronounced aridity and highly localized rock uplift have traditionally been viewed as limits to the dissection of the plateau by bedrock rivers. Recently, however, glacier dynamics and landsliding have been argued to retard headward fluvial erosion into the plateau interior by forming dams and protective alluvial fill. Here, we report a conspicuous clustering of hundreds of natural dams along the Indus and the Tsangpo Rivers where these cross the Himalayan syntaxes. The Indus is riddled by hundreds of dams composed of debris from catastrophic rock avalanches, forming the largest concentration of giant landslide dams known worldwide, whereas the Tsangpo seems devoid of comparable landslide dams. In contrast, glacial dams such as river-blocking moraines in the headwaters of both rivers are limited to where isolated mountain ranges intersect the regional snowline. We find that to first-order, high local topographic relief along both rivers corresponds to conspicuously different knickzones and differences in the type and potential longevity of these dams. In both syntaxes, glacier and landslide dams act as a negative feedback in response to fluvial dissection of the plateau margins. Natural damming protects bedrock from river incision and delays headward knickpoint migration, thereby helping stabilize the southwestern and southeastern margins of the Tibetan Plateau in concert with the effects of upstream aridity and localized rock uplift.

Rock avalanches and the pace of late Quaternary development of river valleys in the Karakoram Himalaya

We discuss the implications of a set of terrestrial cosmogenic nuclide (TCN) ages on blocky, cross-valley deposits of large rock avalanches along upper Indus streams. The dated deposits are key to understanding late Quaternary events that play a major role in landscape evolution in the Karakoram Himalaya. The landslides occurred between 3 and 8 ka ago, challenging existing chronologies of events along Indus streams. The TCN ages may support a mid-Holocene climatic role in preparing slopes for failure, but the balance of evidence suggests that large earthquakes triggered the landslides. Each landslide dammed the Indus or a major tributary and controlled base level and sedimentation for millennia. They produced landforms long regarded as characteristic of the region, including extensive lacustrine deposits, flights of river terraces, epigenetic gorges, and sediment fans. Until the 1990s, most of the landslides were interpreted as moraines; related lacustrine and other sediments continue to be attributed to glacial damming, and stream terraces to tectonic processes. Generally they were seen to originate tens of thousands to hundreds of thousands of years earlier than the new ages require. Instead we argue that they record interactions among different geomorphic processes in landslide-fragmented valleys during the Holocene. Rather than being geomorphic markers of tectonic and climatic events, the landslides have buffered or redirected climatic and tectonic forcing. In such an active orogen, millennia-long episodes of zero net bedrock incision at each site are surprising. However, rates of sedimentation above landslide barriers and erosion controlled by their breaching are close to today9s high measured rates for geomorphic activity. We propose that landslide-fragmented rivers may, in fact, characterize interglaciations and future patterns of upper Indus landscape evolution at time scales of 10 3 to 10 4 years.