CATACLYSM FROM EARTH TO THE KUIPER BELT: A N2-LIQUID MEGA-FLOOD HYPOTHESIS FOR THE FORMATION OF WASHBOARD AND FLUTED TERRAINS ON PLUTO

Surface processes on Earth operate through perpetual actions punctuated by rare cataclysmic events. The 2015 flyby of the New Horizons spacecraft reveals a water-ice surface of Pluto that displays washboard and fluted morphologies characterized by 10-20 km long parallel curvilinear ridges that are ~100 m high and 1 km apart. Although water-ice erosion/deposition, N₂-ice sublimation, and N₂-ice glaciation may explain the ridge formation, none accounts for the spatially associated box-shaped valleys, step-depression pairs along steep-walled valley floors, complex channel networks, variably shaped buttes, and clustered circular depressions without raised rims. Considering a range of Earth analogues involving wind actions, fluvial processes, and glaciation leads us to suggest a likely scenario that the ridges and spatially associated landforms were created by transient N₂-liquid mega-floods during the outbursts of a N₂-liquid lake system that was episodically blocked by moving lobes of N₂ mountain glaciers. This interpretation, similar to the Spokane mega-flood hypothesis of J Harlen Bretz, requires the ridges to represent “giant current ripples”, channels and buttes “channeled scablands”, box-shaped valleys “coulees”, valley-floor step-depression pairs “cataracts”, and circular depressions "turbulence-induced kolk pits”. The hypothesis predicts (1) scattered erratic boulders/blocks in the distal region of the flood plains, (2) streamlined landforms, (3) mountains topped by Alpine-style N2 glaciers surround the interpreted lake (similar to Lake Missoula), and (4) possible pre-flood continental-style ice-sheet glaciation. The simplest fluid-mechanics model for the formation condition of giant current ripples is F ≥ k^1/2tanh^1/2k, where F = u/(√gh) is the Froude number, k =2πh/λ the non-dimensional wave number, g the Pluto gravity, h the flow depth, u the flow velocity, and λ is the ripple spacing. Using the ridge relief of ~100 m as the minimum flow depth and the ridge spacing of ~1 km to constrain the wave number, the estimated flow velocity u is >6 m s^-1. The mega-flood hypothesis implies a transient warmer climate of Pluto in the past and the role of cataclysm in shaping the landscape of solar-system bodies beyond the Earth.