The 20 black runs in the Alps whose steepest stretch is the gentlest. By the ATUDEM and AFNOR criteria, a gradient over 40% is black-run terrain; Gatterl at Zugspitze tops out at 21% (12°) over its steepest 50 m. Official grades also weigh width, exposure and snow, so a gentle black can still be a black.
For every official black run of at least 300 m, its steepest 50 m stretch, measured with the elevation model (about 30 m precision, smoothed against false spikes). Sorted from gentlest. Very short steps may not show.
Gatterl, at Zugspitze: its steepest 50 m stretch is 21%. Next come Canalon - Gran Pista (Monte Bondone, 21%) and Les Balmes (Espace Haute Maurienne Vanoise, 21%).
For every official black run of at least 300 m, its steepest 50 m stretch, measured with the elevation model (about 30 m precision, smoothed against false spikes). Sorted from gentlest. Very short steps may not show. Data from OpenStreetMap via OpenSkiMap.