Lava

Lava is molten or partially molten rock that comes from deep inside a planet like Earth or a moon. It reaches the surface through volcanoes or cracks in the planet's crust. When lava flows out during an eruption, it can be very hot, ranging from 800 to 1,200 °C (1,470 to 2,190 °F).

A lava flow happens when lava pours out during what is called an effusive eruption. Unlike explosive eruptions, which create ash and fragments, lava flows move more smoothly. The lava has a thickness similar to ketchup, which means it is not very runny. However, lava can travel far before it cools and hardens because a solid skin forms on the top, keeping the hot liquid inside warm and flowing.

Etymology

The word lava comes from Italian and is likely based on the Latin word labes, meaning a 'fall' or 'slide'. One of the earliest uses of this word to describe magma coming out of the ground was in 1737, when a writer named Francesco Serao described a "flow of fiery lava" during an eruption of Vesuvius. He compared it to water and mud flowing down the sides of a volcano after heavy rain.

Properties

Solidified lava on Earth is mostly made of silicate minerals such as feldspars, feldspathoids, olivine, pyroxenes, amphiboles, micas, and quartz. These minerals form when lava cools and solidifies.

Silicate lavas contain oxygen and silicon, the most common elements in Earth's crust, along with smaller amounts of other elements like aluminium, calcium, magnesium, iron, sodium, and potassium. The amount of silica in the lava affects its behavior. Lavas with more silica, called felsic lavas, are very thick and usually erupt explosively. Lavas with less silica, called mafic lavas, are thinner and can flow farther. Intermediate lavas have a middle amount of silica, and ultramafic lavas have very little silica.

Morphology

The morphology of lava describes its surface form or texture. Lava can form different shapes depending on how fluid it is. More fluid lava creates flat, sheet-like shapes, while thicker lava forms bumpy, blocky piles.

There are a few main types of lava flows. ʻAʻā lava has a rough, jagged surface made of broken pieces, making it hard to walk on. Pāhoehoe lava is smooth and ropy, often forming tubes as it flows. Block lava is thick and forms angular chunks, moving slowly downhill. Pillow lava forms when lava erupts underwater, creating blob-like shapes as it cools quickly in the water. Each type of lava has its own unique look and behavior.

Main article: Pillow lava

Landforms

Because lava is hot, melted rock, it creates special shapes and features when it flows or erupts. Volcanoes are the most common landforms made by lava. They can be wide and gentle, like shield volcanoes, or tall and steep, like stratovolcanoes.

Lava can also form other interesting shapes. Small hills called cinder cones are made from bits of ash and rock thrown into the air during eruptions. Lava tubes are like tunnels formed when the top of a lava flow cools and hardens, while the lava inside keeps moving. Sometimes, lava can fill up a crater and form a pool called a lava lake.

Lava fountains

A lava fountain is a volcanic event where lava shoots up into the air from a crater, opening, or fissure. It happens without explosions. The tallest lava fountain ever seen was during an eruption of Mount Etna in Italy on November 23, 2013. It reached a steady height of about 2,500 meters, or 8,200 feet, for 18 minutes, and at one point, it shot up to 3,400 meters, or 11,000 feet. Lava fountains are often linked with Hawaiian eruptions.

Hazards

Lava flows can destroy buildings and land in their path, but people and animals usually have time to move out of the way because lava moves slowly. However, sometimes lava can move very fast and catch people by surprise. This happened during an eruption in what is now the Democratic Republic of the Congo in 1977, when a fast-moving lava flow overwhelmed some villages.

Even after lava cools, the land it creates can be unstable and dangerous. Walking on cooled lava requires careful footwear because the surface can be sharp and uneven.

Towns destroyed by lava flows

• The Nisga'a villages of Lax Ksiluux and Wii Lax K'abit in northwestern British Columbia, Canada, were destroyed by thick lava flows during the eruption of Tseax Cone in the 1700s.
• Garachico on the island of Tenerife was destroyed by the eruption of Trevejo (1706) (rebuilt).
• Keawaiki, Hawaii, 1859 (abandoned)
• San Sebastiano al Vesuvio, Italy, destroyed in 1944 by the most recent eruption of Mount Vesuvius during the Allies' occupation of southern Italy (rebuilt)
• Koae and Kapoho, Hawaii, were both destroyed by the same eruption of Kīlauea in January, 1960 (abandoned).
• Kalapana, Hawaii, was destroyed by the eruption of the Kīlauea volcano in 1990 (abandoned).
• Kapoho, Hawaii, was largely inundated by lava in June 2018, with its subdivision Vacationland Hawaii being completely destroyed.

Towns damaged by lava flows

• Catania, Italy, in the 1669 Etna eruption (rebuilt)
• Sale'aula, Samoa, by eruptions of Mt Matavanu between 1905 and 1911
• Mascali, Italy, almost destroyed by the eruption of Mount Etna in 1928 (rebuilt)
• Parícutin (village after which the volcano was named) and San Juan Parangaricutiro, Mexico, by Parícutin from 1943 to 1952
• Heimaey, Iceland, in the 1973 Eldfell eruption (rebuilt)
• Piton Sainte-Rose, Reunion island, in 1977
• Royal Gardens, Hawaii, by the eruption of Kilauea in 1986–87 (abandoned)
• Goma, Democratic Republic of Congo, in the eruption of Nyiragongo in 2002
• Los Llanos de Aridane (Todoque neighbourhood) and El Paso (El Paraíso neighbourhood) on La Palma in the 2021 Cumbre Vieja volcanic eruption

Towns destroyed by tephra

• Pompeii, Italy, in the eruption of Mount Vesuvius in 79 AD
• Herculaneum, Italy, in the eruption of Mount Vesuvius in 79 AD
• Akrotiri, on the Greek island of Santorini, was buried by pumice and ash from the Minoan eruption around 1600 BCE.
• Cerén, El Salvador, in the eruption of Ilopango between 410 and 535 AD
• Sumbawa Island, Indonesia, in the eruption of Mount Tambora in 1815
• Plymouth, Montserrat, in 1995. Plymouth was the capital and only port of entry for Montserrat and had to be completely abandoned, along with over half of the island. It is still the de jure capital.