EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

A catastrophic Late Pleistocene debris flow sourced in the glaciated High Atlas of Morocco

Madeleine Hann1, Jamie Woodward1, Philip Hughes1, and Edward Rhodes2
Madeleine Hann et al.
  • 1Department of Geography, School of Environment, Education and Development, University of Manchester, United Kingdom of Great Britain and Northern Ireland (
  • 2Department of Geography, University of Sheffield, Sheffield, United Kingdom of Great Britain and Northern Ireland

Catastrophic events such as debris flows and big floods are important agents of landscape change in steepland mountain environments. These events can be prominent in paraglacial settings as well as those that are tectonically active.   Since such catastrophic events pose  a significant natural hazard in deglaciating modern settings (e.g. Haeberli et al. 2017), it is useful to better understand analogous events in the recent geological past.

The Tamatert Valley, near the village of Imlil, on the northern slopes of Jebel Toubkal (4167 m a.s.l.) in the High Atlas, holds a valuable record of Quaternary landscape change.  The steepland Tamatert Valley was glaciated during the Pleistocene (Hughes et al. 2018)  and lies on the major Tizi n’Test Fault Zone.

More than 200 well rounded basalt mega-boulders (>2m b axis) have been mapped in the Tamatert Valley catchment (9 km2). Many of the boulders are larger than 5 m (b axis). The mega-boulders are found in the active channel of the Tamatert River, stranded above the modern channel, and embedded in valley-fill deposits. A preliminary chronological framework, combining cosmogenic exposure and luminescence dating, points to deposition of these boulders in the Late Pleistocene. The boulders are porphyritic basalt and lithologically distinct from the local diorite/granite bedrock.  They were transported by a catastrophic flood or debris flow over a distance of more than 3 km from the glaciated basalt source area.

Serendipitously, a debris flow producing a similarly extensive deposit of boulders (up to 3 m b axis) occurred in the neighbouring Mizane Valley in September 2019. Mapping of this modern deposit allows direct comparison with the Late Pleistocene event. Together, these provide valuable insights into the geomorphological significance of high magnitude, large boulder transit events in glaciated, steepland river catchments in the High Atlas. 

Haeberli, W., Schaub, Y. & Huggel, C. 2017. Increasing risks related to landslides from degrading permafrost into new lakes in de-glaciating mountain ranges. Geomorphology, 293, 405–417
Hughes, P.D., Fink, D., Rodés, Á., Fenton, C.R. & Fujioka, T. 2018. Timing of Pleistocene glaciations in the High Atlas, Morocco: New10Be and36Cl exposure ages. Quaternary Science Reviews, 180, 193–213

How to cite: Hann, M., Woodward, J., Hughes, P., and Rhodes, E.: A catastrophic Late Pleistocene debris flow sourced in the glaciated High Atlas of Morocco, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10825,, 2020