What are the two models of volcanic eruptions that are useful to understand in order to comprehend the geologic history of the Valles Caldera?
1. The “toothpaste model,” in which magma slowly and gently flows through weak spots in the earth to the surface. This type of eruption can currently be witnessed in volcanos such as the one on the Big Island of Hawai’i as well as Volcan Arenál in Costa Rica. The volcanic ring fracture domes in the Valles Caldera were formed along the rim of where the earth collapsed in the formation of the Caldera. These domes were formed in a counterclockwise manner understood by the toothpaste model, as lava gently and gradually erupted over the span of 700,000 years. The volcanic ring fracture domes that formed in the Caldera from 1.2 million years ago to 500,000 years ago are, in order of creation, Cerro del Medio, Cerro Abrigo, Cerro Santa Rosa, Cerro Trasquilar, Cerro San Luis, Cerro Seco, and San Antonio Mountain. The remaining ring fracture domes, Cerro la Jara and South Mountain, were formed about 500,000 years ago. Cerro la Jara is the relatively tiny hill that rises in the western Valle Gra
