--- title: Volcanoes: how and where — a lesson of Mova's school · trees and pragmatics description: «Volcanoes: how and where», a lesson of the geography course of Mova's primary school, sentence by sentence with dependency trees and pragmatics. It begins: A volcano is an opening in the crust where melted rock, gas and ash escape from inside the Earth; the mountain is built by its own eruptions pi --- [Mova](https://md.mova.elamur.ai/free/en/) · [this page in HTML](https://mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/) [home](https://md.mova.elamur.ai/free/en/) / [corpora](https://md.mova.elamur.ai/free/en/corpora/) / [school](https://md.mova.elamur.ai/free/en/corpora/school/) / [Geography](https://md.mova.elamur.ai/free/en/corpora/school/geography/) / Volcanoes: how and where # Volcanoes: how and where Lesson 46 of the geography course of Mova's primary school: 15 sentences, each with its syntax tree and pragmatics. The lessons are written for Mova, and their agreed trees are part of Mova corpus 0.4 (CC BY-SA 4.0). How Mova does on its tests: [the lesson at school](https://md.mova.elamur.ai/free/en/school-run/geography/46-volcanoes-how-and-where/). - [0](https://md.mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/0/) — A volcano is an opening in the crust where melted rock, gas and ash escape from inside the Earth; the mountain is built by its own eruptions piling up around the vent. - [1](https://md.mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/1/) — Underground the melted rock is called magma; once it pours out on the surface it is called lava. - [2](https://md.mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/2/) — Open a fizzy drink that has been shaken: the gas rushes out and drags the drink with it; sticky magma full of gas erupts explosively the same way, while runny magma lets the gas escape and just pours out. - [3](https://md.mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/3/) — Most volcanoes sit where plates pull apart or where one plate dives under another, and some, like Hawaii's, sit over a hotspot in the middle of a plate. - [4](https://md.mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/4/) — Most volcanic activity happens unseen on the ocean floor, along the mid-ocean ridges where new crust is made. - [5](https://md.mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/5/) — A volcano is an opening in the crust where melted rock, gas and ash escape from inside the Earth. - [6](https://md.mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/6/) — Melted rock is called magma while it is underground and lava once it pours out on the surface. - [7](https://md.mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/7/) — Most volcanoes sit along plate boundaries, either where plates pull apart or where one plate dives under another. - [8](https://md.mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/8/) — Some volcanoes, like Hawaii's, are in the middle of a plate above a hotspot, a plume of hot rock rising from deep in the mantle. - [9](https://md.mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/9/) — As the plate slides over a hotspot, a chain of volcanoes forms, and the Hawaiian islands get older the further they are from the hotspot. - [12](https://md.mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/12/) — The deadliest danger is a pyroclastic flow, an avalanche of hot gas, ash and rock racing downhill at over 100 km/h. - [13](https://md.mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/13/) — Volcanoes release gases such as water vapour, carbon dioxide and sulfur dioxide, and their sulfur gases can smell of rotten eggs. - [14](https://md.mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/14/) — Most of the Earth's volcanic activity happens unseen on the ocean floor along mid-ocean ridges. - [15](https://md.mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/15/) — A volcano is usually called active if it has erupted in about the last 10,000 years, and extinct if it is not expected to erupt again. - [16](https://md.mova.elamur.ai/free/en/corpora/school/geography/46-volcanoes-how-and-where/16/) — When a huge eruption empties the magma chamber, the ground above can collapse into a giant crater called a caldera. - ← previous: [Tsunamis](https://md.mova.elamur.ai/free/en/corpora/school/geography/45-tsunamis/) - next →: [Famous eruptions and living with volcanoes](https://md.mova.elamur.ai/free/en/corpora/school/geography/47-famous-eruptions-and-living-with-volcanoes/) - ↑ back to [Geography](https://md.mova.elamur.ai/free/en/corpora/school/geography/)