Abstract Of the several types of Quaternary deposits formed by glacial, alluvial and mass-wasting processes, with vast climatic and tectonic significance lake deposits stand out prominently in the Indus valley around the town of Leh. We studied a number of palaeolake deposits between the Zinchan–Indus confluence and Shey village and carried out optically stimulated luminescence (OSL) quartz dating of samples from critical sections. Our results indicate that, during the late Quaternary, the Indus River was dammed at least twice in the narrow gorge downstream of Spituk Gompa, forming a reservoir up to 35 km long in which 20–68 m thick sediments were deposited under fluvial and lacustrine environments. During the older phase, the Indus was blocked by debris of moraines/landslides in the narrow zone near the Zinchan–Indus confluence. The resulting lake existed between c. 125 ± 11 and 87 ± 8 ka during marine isotopic stage (MIS) 5. No evidence of damming material is preserved. Present-day elevations of lake deposits suggest a possible extension of the lake up to Ranbirpura upstream. After the lake breach, the Indus River was again dammed near Phey village by the advancing alluvial fan of the Phyang River. This lake, extending up to Karu, formed at c. 79 ± ka. The lake existed in this phase during c. 72–49 ka, during cold-stage MIS-4. The lake was breached after c. 46 ± 3 ka, however.

ABSTRACT The field trip examines coupled hydrologic and landscape response after the cataclysmic eruption of Mount Mazama to form Crater Lake in the Cascade volcanic arc at ~7627 ± 150 cal. yr B.P. The Williamson River basin, east of Crater Lake and in the rain shadow of the Cascade Range, was buried beneath thick pumice and pyroclastic-flow deposits. The distinctive physical properties of pumice and volcanic ash affect the movement and retention of water and the ongoing evolution of the landscape. Three themes will be explored: (1) post-eruption transition from perched streams to losing streams along the eastern flank of the Cascade Range; (2) filling and catastrophic draining of a lake trapped behind a dam of pyroclastic flow deposits in the Williamson River canyon; and (3) post-eruption faulting and the hydrology of Klamath Marsh.