Geomorphic impacts of new catastrophic events (Case study: Madarsoo basin in northeastern of Iran) Abstract New catastrophic events refer to extreme Hydro-Geomorphic events which take place under influence of global warming and recent technologic activities. In the summer of 2001, an intense thunderstorm in south eastern Caspian Sea triggered a catastrophic flood in the Madarsoo basin .On the basis of the available evidences, the 2001 flood with 1980 m /s peak discharge which affected was the largest flow in the resent centuries. Use of methods including high-resolution aerial photographs and satellite images interpretation, multi-date mapping, hydraulic calculations and field observations made possible the documentation of the geomorphic impacts on the Madarsoo River and its tributaries. The total rainfall (150 mm in 18 hours) aggravated by pre-exiting saturated soils, explain the immediate response of the fluvial system and subsequent destabilization of slops .geomorphologic effects of this catastrophic flooding included: trees up to 2m in diameter were scoured from the main river channels and locally as much as 80% of trees crown cover was removed from riparian zones. The scour of trees exposed the underlying flood plain to macro turbulent scour, leading to extensive removed of flood plain sediments that had accumulated over centuries. Abundant water and sediment supply (land sliding, bank erosion), particularly from small catchment basins resulted in destructive pulses of debris flow and Hyperconcentrated flows. Other hydro-geomorphic impacts of this flood have been drainage network modifications; create new alluvial fans, new meandering pattern and gully development that all of them have been documented by author.

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