The seasonal deposition and sublimation of CO₂ constitute a major element in the Martian volatile cycle. Here, we propose to use the shadow variations of the ice blocks at the foot of the steep scarps of the North Polar Layered Deposits (NPLDs) to infer the vertical evolution of the seasonal deposits at high polar latitudes. We conduct an experiment at a steep scarp centered at (85.0°N, 151.5°E). We show that the average thickness of the seasonal deposits due to snowfalls in Mars Year 31 is 0.97±0.13 m at Ls = 350.7° in late winter, which then gradually decreases in springtime. The large snow depth measured makes us wonder if snowfalls are more frequent and violent than previously thought. Meanwhile, we show that the average frost thickness due to direct condensation in Mars Year 31 reaches 0.64±0.18 m at Ls = 350.7° in late winter and quasi-linearly decreases towards the summer solstice. Combined, the total thickness of the seasonal cover in Mars Year 31 reaches 1.63±0.22 m at Ls = 350.7° in late winter, continuously decreases to 0.45±0.06 m at Ls = 42.8° in middle spring and 0.06±0.05 m at Ls = 69.6° in late spring. These estimates are up to 0.8 m lower than the existing MOLA results during the spring, which can be mainly attributed to MOLA-related biases. In terms of interannual variations, we observe that snow in the very early spring of Mars Year 36 can be 0.36±0.13 m deeper than that in Mars Year 31.