sentences:  Once the volcanic and sedimentary rocks of the Gambier Group were formed, they began to deform, crumple and uplift due to the extreme pressures created by movement of the North American Plate and the tectonic plates in the Pacific Ocean.The large masses of solidified lava that formerly created the volcanic island chain and underwater lava flows yielded by demolishing into massive, mountain-sized blocks while the less dense, thinly layered shale was compressed, folded and crushed between the associated lavas.In contrast, nearby volcanic landforms in the Garibaldi Lake area, such as The Black Tusk, are of relatively recent volcanic origin and form part of a chain of volcanoes called the Garibaldi Volcanic Belt.