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Quaternary fans and terraces in the Khumbu Himal south of Mount Everest: their characteristics, age and formation

Journal of the Geological Society

By:
, , and
DOI: 10.1144/0016-764904-157

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Abstract

Large fans and terraces are frequent in the Khumbu Himal within the high Himalayan valleys south of Mt. Everest. These features are composed of massive matrix- and clast-supported diamicts that were formed from both hyperconcentrated flows and coarse-grained debris flows. Cosmogenic radionuclide (CRN) exposure ages for boulders on fans and terraces indicate that periods of fan and terrace formation occurred at c. 16, c. 12, c. 8, c. 4 and c. 1.5 ka, and are broadly coincident with the timing of glaciation in the region. The dating precision is insufficient to resolve whether the surfaces formed before, during or after the correlated glacial advance. However, the sedimentology, and morphostratigraphic and geomorphological relationships suggest that fan and terrace sedimentation in this part of the Himalaya primarily occurs during glacier retreat and is thus paraglacial in origin. Furthermore, modern glacial-lake outburst floods and their associated deposits are common in the Khumbu Himal as the result of glacial retreat during historical times. We therefore suggest that Late Quaternary and Holocene fan and terrace formation and sediment transfer are probably linked to temporal changes in discharge and sediment load caused by glacier oscillations responding to climate change. The timing of major sedimentation events in this region can be correlated with fans and terraces in other parts of the Himalaya, suggesting that major sedimentation throughout the Himalaya is synchronous and tied to regional climatic oscillations. Bedrock incision rates calculated from strath terrace ages average c. 3.9 mm a−1, suggesting that the overall rate of incision is set by regional uplift.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Quaternary fans and terraces in the Khumbu Himal south of Mount Everest: their characteristics, age and formation
Series title:
Journal of the Geological Society
DOI:
10.1144/0016-764904-157
Volume
163
Issue:
2
Year Published:
2006
Language:
English
Publisher:
Geological Society of London
Contributing office(s):
Coastal and Marine Geology Program
Description:
17 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of the Geological Society
First page:
383
Last page:
399
Country:
Nepal
Other Geospatial:
Imja Khola Valley, Khumbu Himal, Mount Everest
Scale:
25000