Complex sentence: However, in the case of San Rafael Glacier, Chile a switch from retreat (1945-1990) to advance (1990-1997) was noted (Warren, 1993), current examples of this retreat are Columbia Glacier and Guyot Glacier.
Split into simpler sentences: However, in the case of San Rafael Glacier, Chile, a switch from retreat (1945-1990) to advance (1990-1997) was noted (Warren, 1993). Current examples of this retreat are Columbia Glacier and Guyot Glacier.