Mount Warning is the central volcanic remnant of an ancient shield volcano, the Tweed Volcano, which would have been about 1,900 m (6,200 ft) above sea level or just under twice the height of the current mountain. This volcano erupted around 23 million years ago. As the mountain’s central vent cooled it shrank, forming a depression at the top that has greatly eroded.
Today the vast areas that were part of the volcano include many mountains and ranges at some distance from Mount Warning, and include the Border Ranges, Tamborine Mountain, the McPherson Range and both the Lamington Plateau and Springbrook Plateaus. The erosion caldera formed since this eruption is easily visible around the summit and forms the rim of the Tweed Valley.
