Volcanoes are fascinating geological structures that connect the Earth's deep interior to its surface. These gigantic natural chimneys are not only responsible for sculpting imposing volcanic landscapes, but they have also influenced human history through their eruptions. To better understand their behavior, geology classifies them into different types according to various criteria. Among these, hydromagmatic , fissure, and subterranean volcanoes stand out , exhibiting unique characteristics in both their formation and eruptive activity.
This classification allows us to analyze the origin, eruptive dynamics, and associated risks of each type, which is fundamental for natural disaster prevention and land-use planning. Furthermore, understanding historical eruptions helps us grasp the real impact these phenomena have on the environment and the population. In this article, we take you on a comprehensive geological journey to discover how volcanoes are classified, their main types, and real-world examples that offer important lessons. If you'd like to delve deeper into this topic, we invite you to read about volcanism and its importance.
How are volcanoes classified?
Volcanoes can be classified using various geological and volcanological criteria. Among the most important are:
- According to the type of eruption: magmatic, phreatomagmatic or phreatic.
- Due to its shape and structure: shield, stratovolcano, cinder cone, dome, etc.
- According to your activity: active, inactive or extinct.
- By the type of lava and products emitted: basaltic, andesitic, dacitic or rhyolitic.
More specific classifications include hydromagmatic volcanoes , fissure volcanoes , and subglacial or underground eruptions , which fall under the eruptive types defined by the way magma and other elements, such as water, interact. To better understand the different characteristics, you can consult the article on types of volcanoes.
Volcanic eruptions: explosive and effusive
One of the key aspects in volcanology is differentiating between explosive and effusive eruptions :
- Explosives: They are characterized by the violent release of solid fragments, gases, and ash. This occurs when the magma is viscous and has a high silica content, which traps gases and generates pressure.
- effusive: The magma is fluid and low in gases. Lava flows gently from the crater or fissure, forming extensive flows but without large explosions.
Hawaiian volcanoes, for example, represent a clear type of effusive eruption, while Plinian or Pelean eruptions involve explosive eruptions of great destructive power. Understanding these mechanisms is crucial, and for more information on their classification, you can read the article about Mount Tambora.
Magmatic eruptions: classification and examples
These eruptions occur when magma rises to the surface, generating different types of volcanoes depending on their behavior. Let's look at the main ones:
Plinian eruptions
These are the most violent and destructive eruptions. They are characterized by eruptive columns that can reach between 20 and 30 kilometers in height. They alternate between explosive and effusive phases, with the projection of ash, gases, lava, and pyroclastic material. A historical example was the eruption of Mount Vesuvius in 79 AD , which buried Pompeii and Herculaneum. These eruptions are also informative for the study of dormant volcanoes, which you can explore further here in Exploring Dormant Volcanoes.
Other Plinian volcanoes include Teide (Spain), Popocatépetl (Mexico), Fujiyama (Japan) and Mount St. Helens (USA).
Pelean eruptions
They are named after the Mount Pelée volcano in Martinique. These are extremely explosive eruptions, with highly viscous magma clogging the vent. The eruptions generate pyroclastic flows or plumes of fire capable of destroying everything in their path. The 1902 eruption devastated the city of Saint-Pierre. This type of activity is vital for understanding volcanism and igneous rocks.
Vulcan eruptions
The less fluid and more viscous magma causes the crater to clog, building up pressure and triggering violent explosions. The lava fragments rapidly, generating dense ash clouds and volcanic bombs. They often form steep cones. An example: the Vulcano volcano in the Lipari Islands.
Strombolian eruptions
These eruptions alternate between gentle explosive phases and lava flows. The lava is more viscous than in Hawaiian volcanoes but retains some fluidity. Layered cones known as stratovolcanoes are formed. The Stromboli volcano in Italy is an example of this type and has been active for centuries. To better understand its eruptive activity, you can learn more about lava here.
Hawaiian eruptions
Magma emerges through fissures or volcanic tubes in continuous flows of very fluid lava with little gas. These are the quietest eruptions and are associated with volcanoes that have low slopes and large areas . A prime example is the volcanoes of Hawaii, such as Kilauea.
Icelandic or fissure eruptions
This type of eruption occurs along large cracks or fissures in the Earth's crust, through which highly fluid lava emerges. The lava flows spread out, forming thick volcanic plateaus. Well-known examples include the Deccan Plateau in India and the Laki fissure in Iceland.
Phreatomagmatic eruptions: when magma mixes with water
This type of eruption is generated by the interaction between magma and water (from seas, lakes, or groundwater). This sudden mixture produces high-pressure steam that results in violent explosions. Three subtypes are identified:
Surtseyan eruptions
They occur in shallow waters (such as the sea or lakes) and produce explosions due to the direct contact between magma and water. Their name comes from Surtsey Island (Iceland), which was formed in 1963 after an eruption of this type. They can even form new volcanic islands . These eruptions are especially interesting for studying the origin of new islands.
Underwater eruptions
Very common but barely visible. Water pressure prevents gases from being easily released. They usually go unnoticed, except when there is a large release of magma or when they occur in lakes, where their effects are more noticeable.
Subglacial eruptions
They develop beneath large ice sheets , such as glaciers. Magma melts the ice and accumulates water, which can generate explosions or form subglacial lakes. This type of eruption is associated with volcanoes in Iceland or Antarctica. They typically have flat summits and steep slopes.
Phreatic eruptions: without the presence of magma
Phreatic eruptions are volcanically explosive eruptions without magma being released . They occur when water comes into indirect contact with a volcanic heat source, such as magma deep underground, and suddenly turns to steam, generating a large explosion.
This type of eruption throws water, ash, rocks, and steam into the air but does not produce lava. Although less spectacular, they can be very dangerous because they often lack clear warning signs.
Emblematic cases of volcanic eruptions
Below, we review some of the most documented eruptive events that perfectly illustrate the different types of volcanoes and eruptions:
Quizapu Volcano (Chile, 1932)
A Plinian eruption that launched a 30 km high ash column , affecting regions of Argentina and Brazil. It caused significant socioeconomic damage and a global decrease in temperature in the Southern Hemisphere.
Hudson Volcano (Chile, 1991)
A massive explosive eruption, with a dispersion of 4 km³ of tephra that reached over 1200 kilometers. It caused severe damage in Patagonia, affecting livestock and causing desertification.
Planchón-Peteroa Volcano (Argentina-Chile, 1991)
A phreatomagmatic eruption created a new crater and dispersed ash to a height of less than 1000 meters. Although of low intensity, it had a significant impact on livestock and prompted precautionary evacuations.
Lascar Volcano (Chile, 1993)
Subplinian eruption with an eruption column measuring up to 23 km. It dispersed ash as far away as Argentina and caused pyroclastic flows in Chile. This event was one of the largest in northern Chile.
Chaitén Volcano (Chile, 2008)
An explosive eruption occurred after more than 9000 years of dormancy. The formation of a silica dome and its subsequent collapse generated pyroclastic flows and lahars. The city was completely evacuated.
Puyehue – Cordón Caulle Volcanic Complex (Chile, 2011)
A fissure eruption with an eruptive column up to 14 km high and ashfall occurred in Argentina. The Bariloche airport was closed for 7 months. There were also pyroclastic flows and continuous emissions for months.
Copahue Volcano (Argentina-Chile, 2012)
The eruption began as a hydromagmatic eruption that evolved into a Strombolian one. A pyroclastic cone formed within the crater, and ashfall was recorded up to 50 km away. The town of Caviahue was temporarily evacuated.
Calbuco Volcano (Chile, 2015)
A violent sub-Plinian eruption produced a 17,5 km ash column . Pyroclastic flows, lahars, and mass evacuations occurred. In Argentina, ashfall caused air travel disruptions and damage to livestock.
These events demonstrate that classifying volcanoes according to their eruptive behavior is an essential tool for studying and managing volcanic risk. From gigantic Plinian explosions to silent, extensive Hawaiian-type eruptions, each type of volcano represents unique geological dynamics with equally diverse consequences.
