Simplify the following text for a Grade 10 native English-speaking person.
Original: 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 .
Simplified: 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 .