Ten Fascinating Facts About Volcanoes
© John Seaton Callahan 2050 words
Volcanoes are one of the most spectacular natural phenomena on earth. The smoke plumes, ash falls and lava flows of volcanic activity worldwide have captivated the attention of humans for thousands of years.
It is only in recent decades that the basic manifestations of volcanic activity have been explained by science. Previously, most volcanic activity including earthquakes, eruptions, and lava flows were considered to be the work of the gods and beyond human comprehension.
While specialist volcano scientists still cannot predict volcanic eruptions with any degree of certainty, many volcanic processes and phenomena are now well understood and documented.
Fire and Ice
Volcanoes occur worldwide, including in the polar regions. While it is common knowledge that the lava or molten rock that flows from a volcano during an eruption is very hot, eruptions can occur in very cold places also.
The southernmost continent of Antarctica has more than 100 volcanoes, some of them active above the ice layer that covers the continent and many of them classified as sub-glacial, as active under the ice sheet.
The cold island of Iceland in the north Atlantic is one of the most volcanically active places on earth, with one or more volcanoes in an almost continuous state of active eruption at any given time, including underwater.
Thick and Thin
The molten rock ejected from volcanoes is called “lava” and varies greatly in temperature and chemical composition. While all lava is considered to be igneous rock, lavas that are lighter in color are generally higher in silica content and lavas that are darker in color are higher in basalt content. Lava can also vary greatly in temperature, with relatively cooler, slower moving, rougher lava having the name of A’a and hotter, smoother, faster-flowing lava having the name of Pahoehoe.
The names are Polynesian, reflecting the volcanic origin of the Hawaiian islands in the Pacific Ocean, which have volcanoes featuring both types of lava.
Heavy and Light
Lava can also have different densities after it cools into rock, from light enough to float on water to a very heavy and dense stone, used by the Polynesians and other cultures to make carving tools. The ultralight form of cooled lava is called pumice and forms when highly gaseous lava is ejected from the volcano and cools quickly, trapping the gas within the stone. Great rafts of pumice are occasionally seen floating in the oceans of the world following underwater volcanic eruptions and are considered a hazard to navigation.
Pumice also forms on land, like around the rim of the caldera of Santorini Island in Greece and many other Greek islands, where it is mined commercially and sold as beauty aid, the skin-scrubbing “Pumice stone”.
The extremely dense and heavy forms of basaltic lava are rare and only found in a few locations, among them several islands in the Pacific Ocean. This type of basaltic lava has cooled quickly, with the molecules organized in a compact pattern, which is both heavy and dense.
One of the locations for this fine-grained basaltic rock was the remote extinct volcano on Pitcairn Island. The quarry here was mined extensively by Polynesians and the stone traded over a vast area of thousands of miles across the South Pacific from Tahiti to Rapa Nui (Easter Island). This stone was prized for making tools, specifically an adze that could hold an edge similar to a metal tool and efficiently cut and shape hardwoods to make the great sailing canoes the Polynesians used to colonize the Pacific.
High and Low
Volcanoes can range in size from gigantic, the largest mountain in the world, to quite small; cinder cones rising from level ground. The largest mountain in the world by volume is Mauna Kea on the Big Island of Hawaii, a dormant volcano which rises more than 10 000 meters (32 808ft) from the bottom of the Pacific Ocean.
Mauna Kea is a shield volcano, having last erupted more than 4 000 years ago, but as with all dormant volcanoes, it could wake up at any time and begin a new cycle of eruptions.
The flanks of Mauna Kea and many other large volcanoes worldwide are dotted with small cinder cones, where minor eruptions have taken place. Any one of these cinder cones could eventually become the main lava vent, leading to a new large volcano over millions of years of eruption activity.
Composite or Shield
Two of the most common types of volcanoes are composite, or stratovolcanoes and shield volcanoes. A good example of the composite type is Mount Fuji in Japan, with the classic cone shape silhouette built over millions of years of eruption activity.
Composite volcanoes can attain heights of over 8 000 meters (26 246 feet) particularly in subduction zones like the Andes mountains of South America and the long subduction arc of the remote Aleutian Islands in the North Pacific ocean.
An example of a shield volcano, built from millions of years of volcanic activity of hot, fluid and flowing lava known as pahoehoe, is Mauna Kea on the Big Island of Hawaii, the world’s largest mountain by volume.
Shield volcanoes are characteristic of “hot spot” volcanic activity as per the Hawaiian Islands and the Galapagos Islands in the Pacific Ocean, where a tectonic plate moves over a hot spot in the earth’s mantle.
Shield volcanoes formed over the magna from the earth’s mantle, like Mauna Kea in Hawaii and Fernandina in the Galapagos, have layered accumulations of very hot and smooth lava over millions of years.
Dangerous or Safe
Volcanoes can range from viewable by nearly anyone at very close proximity to highly dangerous and experts-only viewing at any range. An example of a relatively safe volcano that nearly anyone can view at close range is the lava lake within the crater at Kilauea Volcano on the Big Island of Hawaii.
Pre-pandemic, thousands of visitors per day could stand near the edge of Kialuea Caldera and peer into Halemaʻumaʻu crater for a view of glowing hot lava during an eruption phase in comfort and safety.
A not so safe volcano would be Mount Merapi on the island of Java in Indonesia, which in terms of lava volume, has been the most active volcano worldwide in the last millenia. Frequent eruptions from Merapi have killed hundreds of local residents, who persist in living in close proximity to the highly active volcano because the exceptionally fertile soil of the area is ideal for growing rice and other crops.
Gods and Goddesses
Before scientists were able to explain the various processes of volcanism, volcanic activity was attributed to a variety of gods and goddesses worldwide.
Vulcan was the god of fire and volcanism in the ancient Roman world, with a forge under Mount Etna on Sicily. Activity making weapons for the gods in Vulcan’s forge was responsible for the frequent eruptions of smoke, ash and lava from Etna, then as now one of the world’s most active volcanoes.
Perhaps the best known volcano goddess worldwide is the Hawaiian deity Pele, who is credited with nothing less than the creation of all the major Hawaiian islands. After being evicted from her father’s home in Tahiti due to alleged sexual indisretions with her sister’s husband, Pele came north to Hawaii in a voyaging canoe. She eventually made her home on Mauna Kea on the Big Island where she resides to this day in spirit at Kilauea, one of the world’s most active volcanoes and is venerated by residents and visitors alike.
Above Water and Under Water
Most of the volcanoes that are studied by scientists and viewed by visitors are above ground, but many volcanoes are constantly erupting unseen worldwide. These are underwater volcanoes, located beneath the oceans. The spectacular eruption and tsunami event on January 15, 2022 of the Hunga Tonga-Hunga Ha‘apai volcano in Tonga was an underwater eruption of massive magnitude, perhaps the largest volcanic event on earth since Krakatoa in 1883.
Scientists are not certain yet exactly what happened on January 15th, but with the eruption recorded in detail by several orbiting satellites and many other instruments, this is likely to be the most documented underwater volcanic eruption in history.
The most active volcano in Europe and one of the most active above-ground volcanoes worldwide is Mount Etna on the island of Sicily in Italy. Along with the potentially deadly Mount Vesuvius in the Naples region, these two Italian volcanoes are two of the most intensely monitored volcanoes in the world. Both Etna and Vesuius bristle with a broad array of sensors, from instruments monitoring earth tremors to sensitive thermometers measuring miniscule changes in temperature, all designed to give scientists the data they need to keep nearby populations safe from any pending volcanic activity.
Rift Zone or Subduction
The different types of volcanoes can occur in many different environments on earth with two of the most common being subduction zone volcanoes and rift zone volcanoes.In the case of a subduction zone volcano, a plate of the earth’s crust is being forced under another plate of crust in a subduction zone as per the Indian ocean coastline of Indonesia and the coast of Chile and Peru in South America.
As the wet underwater portion is forced downward toward the mantle, it gets very hot. The trapped water becomes steam and forces its way to the surface, creating microfissures in the overlying rock, which can eventually become channels for rising magma as a volcano is created.
Another common type of volcano is a rift zone volcano, in which a split in the earth's crust fills with magma from the mantle, which is ejected as lava, forming a volcano. The island of Iceland is a classic example of a collection of shield volcanoes over a rift, all created by the hot, fluid lava from the same crack in the earth’s crust being ejected through different vents, including underwater.
Active or Dormant
One question about volcanoes that has perplexed observers from cave-dwelling Neanderthals to highly educated scientists is if a volcano is active or dormant.
While it may be obvious with many volcanoes, with others it is not apparent at all. It is common for a volcano that has shown no sign of activity in living memory to suddenly erupt with a shower of smoke and ash, or a large flow of lava.
The large shield volcano on the island on La Palma in the Canary Islands of Spain, which had been dormant for over 50 years, suddenly returned to life with a major eruption in September 2021 catching residents and scientists by surprise. The resulting lava flow destroyed millions of euros in property as the molten rock made its way down the slopes of the mountain to the Atlantic Ocean.
Another volcano that is apparently dormant but could wake up at any time with a new round of volcanic activity is Haleakala on the island of Maui in Hawaii. With the last eruption of Haleakala occurring as recently as 1600, scientists are certain the volcano can and will erupt again, but they don’t know exactly when.