GEOMORPHIC RESPONSE OF A LONG CHANNEL TO MODERN, DECADES-LONG, CONTINUOUS BASE-LEVEL LOWERING: NAHAL HAARAVA, THE DEAD SEA

Geomorphic response to base-level lowering dominates landscapes evolution, among them the formation of valleys across continental shelf. Here, we utilize the unprecedented detailed data on the newly incising, kilometers-long, perennial reach of Nahal (Wadi) HaArava that responds to a dramatic, rapid, and continuous lowering of its base-level, the Dead Sea (~30 m during the last ~35 years; ~1 m yr^-1 in the last two decades). The detailed documented changes in the channel during the last decades point to the factors controlling channel evolution in this continuous disequilibrium state. High-resolution LiDAR-based DEMs, aerial and ground photographs, Landsat imagery, and field observations were applied in this sub-annual to decade-long documentation of channel changes including past longitudinal profiles, width, sinuosity, and knickpoint retreat. We identified three stages of channel evolution, which were primarily controlled by the evolving slope at the channel mouth and lithology. These include (a) lengthening and minor incision, maintained by rapid delta progradation on top of relatively low slopes of the emerging shelf-like southern Dead Sea basin. (b) Spatially discontinuous evolution, triggered by steeper mouth slope, in which lithologically (rock salt) induced vertical knickpoints divided the channel to aggressively incising, narrow, and meandering reach downstream and upstream reaches without changes. (c) Spatially continuous evolution following the rapid knickpoint retreat phase; in this phase, the entire studied channel responded to the high mouth slopes, incising relatively homogeneous substrate. i.e. the channel shifted from vertical knickpoint retreat phase to a more diffusive phase along the entire channel.