Una volcanic caldera It is a deep subsidence of the Earth's surface caused by various geographic factors associated with volcanic eruptions. It has a more or less circular structure with a relatively wide base and vertical walls, very similar to an impact crater, but large.
In this article we are going to tell you everything you need to know about the volcanic caldera, its origin, characteristics and importance.
Key features
These are some of the processes that give rise to the volcanic caldera:
- The collapse of a magma chamber, that is, the deposition of a large amount of lava or magma. This process takes place when a volcanic mansion reaches a very high altitude, becomes unstable and finally collapses towards the earth's surface. This is the case, for example, of Las Cañadas del Teide in Tenerife (Canary Islands, Spain).
- swooping explosions, which occur when a very fluid and hot basaltic or alkaline magma rises and hits the reservoir on its way, the reservoir is under enormous pressure and therefore turns into steam. Thus, a large explosion is generated. This is the case, for example, of the Bandama crater on the Spanish island of Gran Canaria.
- Seepage of concentrated lava in the crater, gushing outwards. This is the case, for example, of the Caldera de Taburiente on La Palma, Canary Islands, Spain.
There is a direct relationship between the fluidity or viscosity of the lava, the height and slope of the volcanoes and the size of the eruptions they produce:
- Volcanoes with very hot and flowing lava they tend to produce cones with decreasing slopes, very elongated and quiet eruptions. This is the case with the volcanoes of Hawaii, which often form calderas.
- Volcanoes with relatively cold and viscous lava they form steep cones and steep slopes.
- Volcanoes with too viscous lava form Pelius eruptions, in which the lava solidifies rapidly, generally covering the volcano up to the crater. It forms a volcanic hiss (also known as a volcanic neck or volcanic plug): it forms when the temperature or pressure of the magma is low, or the pressure drops sharply, and the lava is cold enough to solidify quickly and violently. The magma is obtained as it emerges towards the surface, and in later stages it is in a liquid state and subjected to the enormous pressure of the depths of the volcano.
Types of volcanic caldera
Hawaiian volcanoes
Strictly speaking, a boiler is a proportionally larger than normal boiler with quite fluid and hot lava and non-explosive and very prolonged eruptions, as occurs in the volcanoes of Hawaii. The lava lake that forms inside the crater is formed by very hot and fluid basaltic lava, therefore it has a very low silica content. The surface of the caldera forms the crust when it comes into contact with the outside world, but the lava always remains in the shallow layers below it.
The irregular crust within the caldera occurs during the quieter intervals of its eruptive history, while the rim slopes outward very gently. The lake that later formed in the now dormant crater was named Mars.
sinking boiler
When the crust that forms on the surface of the caldera sinks into the liquid lava as its density increases as it cools, the level of the caldera descends and forms a steep ring-shaped slope around it, as seen above on the southern edge of Teide, it can be seen on satellite images (in Las Cañadas del Teide) and photographs of this volcano.
Before the cone subsides, magma can pour down from the top of the chamber, known as a volcanic climax. This subsidence in the lava, in turn, creates a volcanic cone on the side of the caldera, the material of which is formed by the upwelling of eruptive material, created as pressure builds. Cool on the surface of the kettle. This volcanic cone forms a kind of safety valve, expelling pyroclastics (ash, bombs, volcanic rock, sand and volcanic glass) that compensate for the drop in the level of the crater.
This is what formed Mount Teide (and thus later rose as the crater level fell) and the volcanic cone seen at Aniakchak crater in Alaska. A schematic diagram of the formation of the caldera shows us the process. In the case of Mount Mazama, whose eruption formed Crater Lake (in Oregon, USA), we see that the cones that formed Wizard Island formed after the caldera collapsed and cooled. As lava becomes impermeable as it cools, lakes can form. This lake is different from the crater, on the steep slopes around the crater.
Calderas emptied by lava flows
This is the case of the Caldera de Taburiente in the Canary Islands of La Palma. Although the interior of the crater still contained more or less liquid lava, the crater walls split open at one point and the interior lava poured out rapidly, forming what is now known as Barranco de Las Angustias. For this reason, the crater walls are almost vertical because the lava level drops very quickly. The interior slope of this crater, almost one kilometer in an almost vertical direction, It can be seen in this image from the Balcón de Taburiente.
The same happened with La Caldereta, a smaller crater on the east coast of the island of La Palma, whose spillage to the north provided the necessary foundations for the construction of the city of Santa Cruz de la Palma. Today, even La Caldereta itself is urbanized and inhabited.
Finally, most volcanoes in the Galapagos Islands, especially those on Fernandina Island and elsewhere, are subsidence calderas, and in most cases the subsidence is due to lateral overflow of the subsoil, which is why the volcanoes the level of lava inside the mouth falls.
I hope that with this information you can learn more about the volcanic caldera in its characteristics.