Complex sentence: The geology of the park was also heavily influenced by the glacial affects of the ice age: a large glacial lake, water that was held in place by a glacier, broke about 140,000 years ago.
Split into simpler sentences: The geology of the park was also heavily influenced by the glacial affects of the ice age. A large glacial lake, water that was held in place by a glacier, broke about 140,000 thousand years ago.