Which mechanism causes fjord sill formation at the mouth of a glacial valley?

💡 Explanation

When a glacier reaches the coast, it deposits a terminal moraine, composed of eroded sediment, at its furthest extent, creating a raised sill because sediment accumulation slows down. Therefore terminal moraine sediment deposition results, rather than isostatic rebound, tidal erosion variation or meltwater channel deposition, which operate over longer time scales, or require different conditions.

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