Lewis A. Owen

The role of the Indian summer monsoon and the mid-latitude westerlies in Himalayan glaciation; review and speculative discussion

New dates for late Quaternary glaciations in the Himalayas show that, during the last glacial cycle, glaciations were not synchronous throughout the region. Rather, in some areas glaciers reached their maxima at the global glacial maximum of c. 18–20 ka bp, whereas in others glaciers were most extensive at c. 60–30 ka bp. Comparison of these data with palaeoclimatic records from adjacent regions suggest that, on millennial timescales, Himalayan glacier fluctuations are controlled by variations in both the South Asian monsoon and the mid-latitude westerlies.

Timing of multiple late Quaternary glaciations in the Hunza Valley, Karakoram Mountains, northern Pakistan: Defined by cosmogenic radionuclide dating of moraines

Moraines and associated landforms in the upper Hunza Valley, Karakoram Mountains, northern Pakistan, provide an excellent record of multiple glaciations. During the late Quaternary, glaciers advanced at least eight times. By using 10 Be and 26 Al surface-exposure dating on moraine boulders and scoured bedrock, we determined the timing of glaciation for four of these glacial advances: ca. 54.7‐43.2 ka (Borit Jheel glacial stage), ca. 25.7‐21.8 ka (Ghulkin I glacial stage), ca. 18.4‐15.3 ka (Ghulkin II glacial stage), and ca. 10.8‐9.0 ka (Batura glacial stage). For two of the older advances, the Yunz and Shanoz glacial stages, our data set a limit of .60 ka. Although, at present, the uncertainties in dating make it impossible to describe unequivocally the climate processes controlling glaciations in the Hunza Valley, the results suggest that precipitation changes related to oscillations in the southwest Asian monsoonal system combine with cooling that is broadly associated with Heinrich events to cause glacial advances in this region.

Quaternary glacial history of NW Garhwal, Central himalayas

A first account of the Quaternary glacial history is presented for northwest Garhwal, Central Himalaya. On the basis of sediments and landforms, one glacial stage has been recognised. This is called the Bhagirathi Glacial Stage, when extensive valley glaciers advanced down the Bhagirathi valley to Jhala, 40.5 km from the snout of Gangotri Glacier. The ELA depression during this stage was ca. 640 m. The Bhagirathi Glacial Stage is constrained by optically stimulated luminescence dates of ca. 63 ka and 5 ka BP, and this glaciation is considered equivalent to the Last Glaciation elsewhere in the world. The maximum extent of ice occurred ca. 63 ka BP. This, however, does not correlate with the Last Glacial Maximum for the northern hemisphere ice sheets (20−18 ka BP). A series of sharp-crested moraines are present between 1 to 3 km beyond the snouts of most of the present glaciers. These moraines formed during the mid Holocene (<5 ka BP), termed here the Shivling Glacial Advance. Small moraines are inset into these and are dated at about 200 to 300 BP (the Bhujbas Glacial Advance; ca. 300 to 200 BP) and considered equivalent to the Little Ice Age in other parts of the world. ELA depressions of between 40–100 m and 20–60 m occurred during the Shivling and Bhujbas Glacial Advances, respectively. Since the Bhujbas Glacial Advance, there has been progressive retreat of glaciers, initially by downwasting and retreat, and then by simple retreat. This retreat has accelerated during the last few decades. Impressive paraglacial fans are associated with deglaciation representing very rapid resedimentation during and soon after ice retreat.

Beryllium-10 dating of Mount Everest moraines indicates a strong monsoon influence and glacial synchroneity throughout the Himalaya

Moraine successions in glaciated valleys south of Mount Everest provide evidence for at least eight glacial advances during the late Quaternary. Cosmogenic radionuclide (CRN) surface exposure dating of moraine boulders defines the timing of each glacial advance and refines the previous glacial chronologies. The CRN data show that glaciation was most extensive during the early part of the last glacial (marine oxygen isotype stage (MIS) 3 and earlier), but limited during MIS 2 (the global Last Glacial Maximum) and the Holocene. A previously assumed Neoglacial advance is dated to 3.6 6 0.3 ka and the CRN dates confirm a glacial advance ca. 1 ka. These results show that glaciations on the south side of Everest were not synchronous with the advance of Northern Hemisphere ice sheets, yet glaciations within the Himalaya, the worlds highest mountain belt, were synchronous during the late Quaternary. The existence of glacial advances during times of increased insolation suggests that enhanced moisture delivered by an active south Asian summer monsoon is largely responsible for glacial advances in this part of the Himalaya. These data allow us to quantify the importance of global climate change and monsoon influence on glaciation in the Himalaya.

Natural and human-induced landsliding in the Garhwal Himalaya of northern India

After the March 28, 1999, Garhwal earthquake, 338 active landslides, including 56 earthquake-induced landslides, were mapped in a 226-km 2 -study area in the Garhwal Himalaya, northern India. These landslides mainly comprised shallow failures in regolith and highly weathered bedrock involving avalanches, slides, and flows. The total volume of active 33 Ž. landslide debris in the region was estimated to be ; 1.3 million m including 0.02 million m - 2% of the total volume moved during and within a few days of the earthquake. The denudation produced by the active landsliding within the study area is equivalent to a maximum landscape lowering of ; 5.7 mm. If active landsliding persists for a duration of between ; 1 and 10 years, then denudation due to landsliding is in the order of ; 0.6–6 mm a y1 . Approximately, two-thirds of the landslides in this region were initiated or accelerated by human activity, mostly by the removal of slope toes at road cuts, suggesting that human activity is accelerating denudation in this region. Three ancient catastrophic landslides, each involving ) 1 million m 3 of debris, were identified and two were dated to the early–middle Holocene using cosmogenic radionuclide 10 Be and 26 Al. Cosmogenic radionuclide 10 Be and 26 Al were also used to date strath terraces along the Alaknanda River in lower Garhwal Himalaya to provide an estimate of ; 4m m a y1 for the rate of regional denudation throughout the Holocene. Natural landsliding, therefore, contributes ; 5–50% of the overall denudation in this region and is important as a formative process in shaping the landscape. q 2001 Elsevier Science B.V. All rights reserved.

Terrestrial cosmogenic nuclide surface exposure dating of the oldest glacial successions in the Himalayan orogen: Ladakh Range, northern India

Terrestrial cosmogenic nuclide surface exposure dating of moraine boulders and alluvial fan sediments define the timing of five glacial advances over at least the last five glacial cycles in the Ladakh Range of the Transhimalaya. The glacial stages that have been identified are: the Indus Valley glacial stage, dated at older than 430 ka; the Leh glacial stage occurring in the penultimate glacial cycle or older; the Kar glacial stage, occurring during the early part of the last glacial cycle; the Bazgo glacial stage, at its maximum during the middle of the last glacial cycle; and the early Holocene Khalling glacial stage. The exposure ages of the Indus Valley moraines are the oldest observed to date throughout the Himalayan orogen. We observe a pattern of progressively more restricted glaciation during the last five glacial cycles, likely indicating a progressive reduction in the moisture supply necessary to sustain glaciation. A possible explanation is that uplift of Himalayan ranges to the south and/or of the Karakoram Mountains to the west of the region may have effectively blocked moisture supply by the south Asian summer monsoon and mid-latitude westerlies, respectively. Alternatively, this pattern of glaciation may reflect a trend of progressively less extensive glaciation in mountain regions that has been observed globally throughout the Pleistocene.

Timing of Late Quaternary glaciations in the Himalayas of northern Pakistan

Optically stimulated luminescence dating of Late Quaternary glaciogenic sediments was undertaken in critical areas of the Himalayas of northern Pakistan in order to examine the timing of glaciation. The dates demonstrate that several glaciations occurred during the last glacial cycle. In Swat, the Grabral 2 Stade and the Kalam I Stade were dated at ca. 77 ka and ca. 38 ka, respectively. The error on the former date is large and it is conceivable that the moraines may have formed during the early part of Oxygen Isotope Stage 3 rather than during Oxygen Isotope Stage 4. The Kalam I Stade, however, clearly represents a glaciation during Oxygen Isotope Stage 3. The oldest moraines and those at the lowest altitude in the Indus valley at Shatial have an age of ca. 60 ka. These also relate to a major glacial advance during Oxygen Isotope Stage 3. A younger series of moraines, the Jalipur Tillite, and glaciofluvial sands at Liachar in the Indus valley, and moraines at Rampur-Tarshing have ages of ca. 27 ka, ca. 21-23 ka and ca. 15 ka, respectively. These dates show that glaciers also occupied parts of the Indus valley during Oxygen Isotope Stage 2. These dates and the morphostratigraphy show that glaciation in the Pakistani Himalaya was more extensive during the early part of the last glacial cycle and that the local last glacial maximum in Pakistan was asynchronous with the maximum extent of Northern Hemisphere ice sheets. Copyright

Timing and style of Late Quaternary glaciation in northeastern Tibet

Glacial successions in the Anyemaqen and Nianbaoyeze Mountains of northeastern Tibet are reassessed and new glacial chronologies are presented for these regions. Cosmogenic radionuclide and optically stimulated luminescence dating indicates that two glacial advances occurred in marine isotope stage (MIS)-3 and MIS-2. In the Anyemaqen Mountains, a third advance occurred in the Early Holocene. We suggest that glaciation was synchronous in the Anyemaqen and Nianbaoyeze Mountains, as well as in other glaciated areas of Tibet and the Himalaya that are influenced by the Asian monsoon. The maximum extent of glaciation occurred early in the last glacial cycle (MIS-3) during a time of increased insolation when the monsoon intensified and supplied abundant precipitation, as snow at high altitude, to feed high-altitude glaciers. This suggests that precipitation, as snow, is fundamental in controlling glaciation in these regions. However, the occurrence of glacial advances during the insolation minimum of MIS-2 suggests that, despite reduced precipitation at this time, the annual temperatures were cold enough to maintain positive glacier mass balances. The numerically defined chronologies for the Anyemaqen and Nianbaoyeze Mountains presented here provide a framework for comparing glacial advances in other parts of high Asia.

Quaternary glaciation of Muztag Ata and Kongur Shan: Evidence for glacier response to rapid climate changes throughout the Late Glacial and Holocene in westernmost Tibet

The glacial geology of two massifs, Muztag Ata and Kongur Shan, in western Tibet was examined to help define the timing and style of glaciation in the semiarid regions of western Tibet. Remote sensing, geomorphic mapping, and 10Be terrestrial cosmogenic nuclide (TCN) surface-exposure dating of boulders on the moraines and sediment in depth profiles show that glaciers advanced at least 12 times during at least the last two glacial cycles. Over this time, the style of glaciation changed progressively from one that produced ice caps to one that produced less extensive and more deeply entrenched valley glaciers. The timing of the two earliest glaciations is poorly defined, but they likely occurred prior to the penultimate glacial cycle (the Karasu glacial stage) and the early part of the last glacial cycle or during the penultimate glacial cycle (the Subaxh glacial stage). In contrast, the timing of later glacial advances (the Olimde glacial stage) is relatively well defined showing quasiperiodical oscillations on millennial time scales (17.1 ± 0.3 ka, 13.7 ± 0.5 ka, 11.2 ± 0.1 ka, 10.2 ± 0.3 ka, 8.4 ± 0.4 ka, 6.7 ± 0.2 ka, 4.2 ± 0.3 ka, 3.3 ± 0.6 ka, 1.4 ± 0.1 ka, and a few hundred years before the present). These data suggest that since the global Last Glacial Maximum (LGM), the glaciers in western Tibet likely responded to Northern Hemisphere climate oscillations (rapid climate changes), with minor influences from the south Asian monsoon. This study provides the first well-defined glacial geologic evidence to suggest that glaciers in western Tibet respond to rapid climate changes on millennial time scales throughout the Late Glacial and Holocene.

Geological evolution of the southeastern Red Sea Rift margin, Republic of Yemen

The tectonic evolution of the southeastern margin of the Red Sea Rift in western Yemen has been investigated using a multi-disciplinary field study of an east-west transect between Al Hudaydah and Sana9a. Slow subsidence of up to 1 km occurred over the area during a 100 m.y. period before rifting. There was a major episode of flood volcanism between ca. 30 and 20 Ma, and important extensional faulting began after the eruption of the volcanic rocks and ceased before middle to late Miocene sediments and volcanic rocks were deposited unconformably on top of rotated fault blocks on the coastal Tihama Plain. Surface uplift has produced the Yemen highlands, whose highest peak reaches an elevation of 3660 m. This is attributed to plume heating and eruption of >3000 m of volcanic rocks. Apatite fission-track ages indicate early to middle Miocene exhumational cooling ages, postdating the major volcanic phase and contemporaneous with rifting. Volcanism was accompanied by emplacement of subvertical dike swarms, which generally strike north-northwest to northwest, broadly parallel to the Red Sea coastline. Major faults indicate northeast-southwest-directed extension. Large granitic sheets and plutons (up to 25 km wide) intruded the volcanic rocks. Approximately 30 km of extension has taken place across a 75-km-wide zone (β = 1.7) in 6-8 m.y. The relative timing of volcanism followed by extension and uplift does not fit conventional models of passive or active rifting. We suggest that the proto-Red Sea Rift was caused by regional plate stresses that exploited lithospheric weakening caused by the Afar plume. Appreciable doming only occurred after the main episode of volcanism, which suggests that magmas extruded before maximum thermal expansion of the lithosphere took place.