Volcanoes of east-central Baja California

The Volcanoes of east-central Baja California are located on the Baja California Peninsula near the Gulf of California, in the state of Baja California Sur, in Mexico.

The large La Reforma Caldera is located on the eastern coast of the central Baja California Peninsula, facing the Gulf of California, near Santa Rosalia, Baja California Sur. The outer rim of the caldera is defined by dark-colored rocks made out of very fluid lava. A dome of rock in the center of the caldera is a resurgent dome. A resurgent dome is formed as the floor of the caldera is heaved upward by the movement of magma below ground. The lavas surrounding the caldera date to about 1 million years ago.

The Tres Virgenes, a line of three connected volcanoes, collectively known by that name, are west of La Reforma Caldera. La Vírgen, in the southwest, El Azufre in the center, and El Viejo in the northeast. The volcanoes get larger and younger from northeast to southwest. As recently as 6,500 years ago, La Vírgen experienced a Plinian eruption — a huge, explosive event that produces an enormous column of volcanic rock fragments and gas that reaches into the stratosphere. The eruption produced a column that reached at least 18 kilometers into the air and deposited ash and rock fragments over 500 square kilometers. In later stages of the eruption, pyroclastic flows (pinkish rocks) and lahars (mudflows, grayish rocks) from El Azufre Volcano paved the plain to the north all the way to the Gulf of California.

El Aguajito Caldera is north-northeast of Las Tres Vírgenes, where pyroclastic rocks and lava date to between 500,000-800,000 years old. The rim of the caldera is not continuously exposed at the surface, but the rocks have a subtle circular arrangement. Like La Reforma, the northern rim of El Aguajito follows the coastline. The flat-looking rock formations, carved by arroyos, are lava domes, hardened mounds of slow-moving, sticky lava. The topography in the southern part of the caldera is more rugged and irregular. The rocks are a combination of pyroclastic deposits and a slightly more fluid lava than what erupted near the coast.

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