Glossary
Definitions of the main terms in alphabetical order that appear in the book and on our website. You can more easily search for each of the terms by clicking on the letters that appear below and that will take you directly to the section for each of them.
We are working on the English version of the Glossary. Soon there will be more terms!
A
Columnar jointing
A type of lava flow fracturing that, due to its cooling, contracts and breaks in regular shapes, the most common being those with 6 sides, forming hexagons. As the lower levels of the lava flow cool, columns of volcanic rock build up.
Foto: Joaquín Hopfenblatt
Effussive activity
The type of volcanic activity in which the magma reaches the Earth’s surface almost without fragmenting, giving rise to lava flows. It occurs in magmas with low gas content.
Erupción Fagradalsfjall, Toby Elliott, Unsplash License. https://unsplash.com/photos/HNDs26Xh1lI
Erratic block
They are huge rocks that come off the volcano and move while floating on the lava. If they stop, they can block the lava river and divert it.
Explosive activity
Type of volcanic activity in which explosions occur as a result of the expansion of magmatic gases. These explosions expel fragments of magma of different sizes (pyroclasts) to the outside.
Russia’s Sarychev Volcano, NASA, Public Domain. https://en.wikipedia.org/wiki/Explosive_eruption#/media/File:Sarychev_Volcano_edit.jpg
Hot springs
These are mineral waters that come from deep and hot parts of the crust and that come out to the Earth’s surface at a temperature of more than 5°C. In volcanic areas they can reach much higher temperatures, and have historically been used as a type of medicinal therapy.
Zona geotérmica de Waiotapu, Nueva Zelanda (180108-85), GeologyPics https://geologypics.com/search-images/?_sf_s=thermal
Pyroclastic density currents
These are flows of pyroclastic material, block to ash size, plus volcanic gas. They travel at high speed for several tens of kilometers, destroying or burying almost everything in their path. With their extreme temperatures (between 200°C and 700°C) they can start fires and melt snow and ice.
Actividad Volcán de Fuego, Conred Guatemala, Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0). https://www.flickr.com/photos/conred/19339585831
Volcanic bomb
Pyroclasts of greater than 64 mm that is expelled by a volcano during the eruption and can reach many kilometers away.
Geology Department, Wittenberg University, Springfield, Ohio, USA, Attribution 2.0 Generic (CC BY 2.0). https://www.flickr.com/photos/jsjgeology/40918007744
Volcanic cone
Volcanic building with a more or less conical shape and that is built by the accumulation of volcanic materials (both lava and pyroclasts) around the mouth of the volcano.
Volcán Mayon, Filipinas, Rafael Loreto, Unsplash License. https://unsplash.com/photos/vK6E0xSLb9s