The Bridge River Vent was formed during an onset of eruptive activity about 2,350 years ago that ended a long period of dormancy at the Mount Meager massif. Substantially, the Bridge River event was explosive in nature, ranging from Plinian to Peléan activity. This is one of the most recent eruptions in the Garibaldi Volcanic Belt and the largest known explosive eruption in Canada in the past 10,000 years. It had similarities to the 1980 eruption of Mount St. Helens in the U.S. state of Washington and the continuous eruption of Soufrière Hills on the island of Montserrat in the Caribbean. The eruption, which was likely VEI-5 in nature, included a series of eruptive episodes that created a variety of volcanic deposits. They are exposed in cliff sections near the long Lillooet River and comprise the Pebble Creek Formation.