Lava tube in the context of Stóra-Eldborg undir Geitahlíð

A fissure vent, also known as a volcanic fissure, eruption fissure or simply a fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is often a few metres wide and may be many kilometres long. Fissure vents can cause large flood basalts which run first in lava channels and later in lava tubes. After some time, the eruption tends to become focused at one or more spatter cones. Volcanic cones and their craters that are aligned along a fissure form a crater row. Small fissure vents may not be easily discernible from the air, but the crater rows (see Laki) or the canyons (see Eldgjá) built up by some of them are.

The dikes that feed fissures reach the surface from depths of a few kilometers and connect them to deeper magma reservoirs, often under volcanic centers. Fissures are usually found in or along rifts and rift zones, such as Iceland and the East African Rift. Fissure vents are often part of the structure of shield volcanoes.

Nahcolite is a soft, colourless or white carbonate mineral with the composition of sodium bicarbonate (NaHCO₃) also called thermokalite. It crystallizes in the monoclinic system.

Nahcolite was first described in 1928 for an occurrence in a lava tunnel at Mount Vesuvius, Italy. Its name refers to the elements which compose it: Na, H, C, and O. It occurs as a hot spring and saline lake precipitate or efflorescence; in differentiated alkalic massifs; in fluid inclusions as a daughter mineral phase and in evaporite deposits.

Journey to the Center of the Earth (French: Voyage au centre de la Terre), also translated with the variant titles A Journey to the Centre of the Earth and A Journey into the Interior of the Earth, is a classic science fiction novel written by French novelist Jules Verne. It was first published in French in 1864, then reissued in 1867 in a revised and expanded edition. Professor Otto Lidenbrock is the tale's central figure, an eccentric German scientist who believes there are volcanic tubes that reach to the very center of the earth. He, his nephew Axel, and their Icelandic guide Hans rappel into Iceland's celebrated inactive volcano Snæfellsjökull. They then contend with many dangers, including cave-ins, subpolar tornadoes, an underground ocean, and living prehistoric creatures from the Mesozoic and Cenozoic eras (the 1867 edition inserted additional prehistoric material). Eventually the three explorers are spewed back to the surface by the eruption of an active volcano, Stromboli, located in southern Italy.

The category of subterranean fiction existed well before Verne. However, his novel's distinction lay in its well-researched Victorian science and its inventive contribution to the science-fiction subgenre of time travel—Verne's innovation was the concept of a prehistoric realm still existing in the present-day world. Journey inspired many later authors, including Sir Arthur Conan Doyle in his novel The Lost World, Edgar Rice Burroughs in his Pellucidar series, and J. R. R. Tolkien in The Hobbit.

Mazuku (Swahili for "evil winds") are pockets of dry, cold carbon dioxide-rich gases released from vents or fissures in volcanically and tectonically active areas, mixed with dispersed atmospheric air and accumulating in typically low-lying areas. Since carbon dioxide (CO₂) is ~1.5 times heavier than air, it tends to flow downhill, hugging the ground like a low fog and gathering in enclosed spaces with poor ventilation—such as lava tubes, ditches, depressions, caves, and house basements—or in the stratified water layers of meromictic lakes if a water column exists. In high concentrations (≥ 1% by volume), they can pose a deadly risk to both humans and animals in the surrounding area because they are undetectable by olfactory or visual senses in most conditions.

Mazuku primarily occur on the northern shores of Lake Kivu to either side of the twin towns of Goma (Democratic Republic of the Congo) and Gisenyi (Rwanda), where local communities use this term in their vernacular (Kinyabwisha language) to describe the dangerous gases. They believe mazuku occur in cursed locations where invisible forces roam, silently killing people in the night while they sleep. In many places where mazuku occur, CO₂ levels fall during daytime but can rise to significantly dangerous concentration levels of about 90% at night, early mornings, or evening hours, posing a great threat. This is because at night the atmospheric temperature drops and wind speeds significantly reduce. These conditions slow the dispersal of these heavy gases into the atmosphere, allowing them to accumulate in lower-lying areas, such as valleys and depressions.

Lava pillars are common within collapsed sheet flow terrain. Lava pillars are hollow inside forming a pipe-like channel between the bottom and the top of a lava flow. They sometimes coalesce to form walls or can be attached to other pillars by natural bridges.

Lava pillars originate as gaps between lava lobes as a lava flow initially advances. Water that is trapped beneath the flow is heated and channeled upward through these gaps. This cold water promotes rapid growth of the lava crust around the gaps. Then during flow inflation the hollow pillars continue to act as escape-routes for seawater trapped beneath the lava flow, and so the gaps between lobes grow upwards into pipe-like pillars. The height of the lava pillars is a measure of the maximum thickness the lava flow attained. After lava inflation ends and the eruption wanes, the molten interior of the sheet flow typically subsides leaving a series of "bathtub rings" along the sides of the pillars. These rings are formed as the crust on the subsiding lava repeatedly adheres to and then breaks off from the pillar's sides.

Manjanggul (Korean: 만장굴) is a lava tube located in Gimnyeong-ri, Gujwaeup, Jeju City, South Korea. At up to 23 metres (75 ft) wide, 30 metres (98 ft) high and 8.928 km (5½ miles) long, it is the 12th-longest lava tube in the world and the second longest on Jeju Island. It is the only cave of the Geomunoreum Lava Tube System, considered one of the finest lava tube systems in the world. It is regularly open to the public, although a significant portion of the cave is closed to visitors. It is also part of the UNESCO World Heritage Site list, under the item Jeju Volcanic Island and Lava Tubes.

Lava stalactites and lava stalagmites, lava columns, lava flowstone, lava rafts, lava shelves, Among them, a lava column of 7.6 metres (25 ft) is the largest known in the world.