Complex sentence: Geologic studies have shown that The Volcano and its eruptive products were emplaced in the past 400 years; this is well after the last glacial period, which ended about 10,000 years ago.
Split into simpler sentences: Geologic studies have shown that The Volcano and its eruptive products were emplaced in the past 400 years. This is well after the last glacial period, which ended about 10,000 years ago.