Volcanoes are constructive forces in that they create new land, fertilize existing lands and bring many new minerals to the surface of the planet. Volcanoes also bring heat to the areas surrounding them and attract wildlife on land and beneath the sea.
Volcanoes create new land when molten rock, or magma, flows up from inside of the planet. The magma emerges as lava, and as it cools, it solidifies into rock again and creates new land. In the case of island volcanoes, these lava flows extend the edges of the island out into the ocean. However, just as with land-based volcanoes, many developed areas are also covered in lava during the process.
Volcanic rocks, when worn down and weathered into the dirt, create rich soils that are ideal for farming a variety crops. Volcanic eruptions also bring precious metals and minerals to the surface where it can be harvested, such as gold, silver, sulfur and diamonds.
Volcanoes also construct amazing structures at the bottom of the deepest parts of the ocean. These volcanoes often form gigantic underwater structures of condensed minerals, and some grow large enough to reach up and out of the sea to form entirely new islands. Volcanoes are also constructive to scientists and their overall understanding of the internal workings of the planet.