On 15 June 1991, Mount Pinatubo, just 20 miles (32 km) from Subic Bay, exploded with a force eight times greater than the Mount St. Helens eruption. The sun was nearly completely hidden as volcanic ash blotted it out. Volcanic earthquakes and heavy rain, lightning and thunder from Typhoon Yunya passing over northern Luzon resulted in a 36-hour period of complete chaos.