El Tatio Geysers and Hot Springs
The excursion from the Explora Lodge left at 5:00 a.m. on November 25th. The reason for the early start was to arrive at the hot springs prior to sunrise. Prior to the sun coming up, the air temperature is still low and this means that the steam rising from the hot water is more abundant and spectacular (I also found it harder to get a good picture due to all the steam). The ride to El Tatio took about two hours on a very bumpy dirt road. There were five of us in the van, plus the guide and drive. Most of us managed to get some sleep on the ride, despite the road conditions. We arrived at the hot springs prior to sunrise as planned. Once there we were pretty much free to wander around and look at the various pools of steaming and boiling water. As the sun cleared the volcanic peaks to the east, the scene changed rapidly. Many of the pools continued to steam, but the amount was greatly reduced. After sunrise, a small breakfast buffet was served to the guests from the Explora Lodge. After eating breakfast, Kevin Clement and I started hiking across the west side of the valley to some of the hot springs located there. Our van later drove over to pick us up.
The El Tatio geysers and hotsprings are located to the north-northeast of San Pedro de Atacama, at approximately 22°20'S Latitude and 68° W Longitude. The valley in which the hotsprings are located is a north-south oriented, volcanotectonic graben - essentially an elongated depression resulting from both volcanic and tectonic activity. Tectonic activity is defined as crustal deformation due to stresses in the crust which are usually the result of mountain building activity. The limits of this graben are the Tucle horst (tectonically raised block of crustal material) on the west and a chain of Pliocene-Quaternary aged volcanoes to the east. The Tatio graben is filled with volcanic material up to 1,800 meters thick. The main reservior of water is found within the permiable layers of volcanic materials. These permiable volcanic layers are capped by impermiable volcanic material. A series of fractures allow the hot water to reach the surface. The heat source is not known for certain, but may be the result of the cooling of the volcanic materials that were deposited in the graben, or a body of magma beneath the graben which is cooling.
The thermal activity at El Tatio covers and area of approximately 10 square kilometers and occurs in the form of geysers, steaming pools, boiling pools, fumeroles and springs. The water that emerges at the surface has a temperature of 86°C, but has been measured at temperatures of between 160° and 265°C at depth beneath the surface. Water normally has a boiling temperature of 100°C. However, at 4,200 meters elevation the boiling temperature of water is 86°C. The lowest elevation in the graben is just below 4,300 meter. This means that the water that emerges from hot spring is at a high enough elevation and temperature to actually boil. Evidence of this is seen in numerous pools where the water is "bubbling" or boiling. In the case of the geysers, the force of the boiling water, within a restricted conduit, results in the water being propelled above the surface. At the time of the author's visit, only one geyser was active, shooting water approximately 2 meters above the surface. Information from local guides indicate that activity has varied over time and that more geysers have been active in the past. Many of the pools and hot springs have calcium-silica deposits surrounding them. The hot waters beneath the surface dissolve minerals from the volcanic materials and bring these minerals to the surface. Evaporation of the hot water leaves these minerals behind.
Parts of the information above have been summarized from the following source: Marinovic, N. and A. Lahsen, 1984, Hoja Calama, Region de Antofagasta, Carta geologica de Chile No. 58, 1:250,000. Servicio Nacional de Geologia y Mineria, ISSN 0716-0194.