Input (grade 13): Periodically the glacier advances over the L-shaped "Lago Argentino" ("Argentine Lake") forming a natural dam which separates the two halves of the lake when it reaches the opposite shore.
Output (grade 9): Periodically the glacier advances over the L-shaped "Lago Argentino" ("Argentine Lake"). when it reaches the opposite shore, it forms a natural dam which separates the two halves of the lake.