EXTRUSIVE VOLCANIC FEATURES

Extrusive volcanic features.

Craters

 Crater is a bowl shaped depression at the top of a volcano caused by past volcanic eruptions. Craters can be thought of as the volcano “blowing its lid” where volcanic materials, such as ash, lava and rock fragments, are released. A volcanic crater is relatively small, usually spanning about a half a mile in diameter or less, and can fill with water to form a crater lake.

Caldera If a volcanic eruption causes the magma chamber to empty, the volcano can implode, forming a larger depression known as a caldera. So a caldera can be defined as a large volcanic crater formed by the collapse of the central part of the volcano.

The term 'caldera' comes from the Latin language and means 'cooking pot.' While a caldera would make an awfully big pot of soup, you can see how the large bowl shape of a caldera, along with the smoky look of the ash cloud rising above it after an eruption, could prompt the name.

Cinder Cone Volcanoes

These are the simplest type of volcano which occusr when particles and blobs of lava are ejected from a volcanic vent. The lava is blown violently into the air and the pieces rain down around the vent.

Composite Volcanoes

Composite or strato volcanoes these volcanoes have a conduit system inside them that channels magma from deep within the Earth to the surface. They can have clusters of vents, with lava breaking through walls, or issuing from fissures on the sides of the mountain. With all this material coming out, they can grow thousands of meters tall. As we’ve seen with the famous Mount Saint Helens, composite volcanoes can explode violently. : Mount Rainier, Mount Fuji, and Mount Cotopaxi, for example.

Shield Volcanoes:

These are large, broad volcanoes that look like shields from above. The lava that pours out of shield volcanoes is thin, so it can travel for great distances down the shallow slopes of the volcano. These volcanoes build up slowly over time with hundreds of eruptions creating many layers. Perhaps the best known shield volcanoes that make up the Hawaiian Islands, especially Mauna Loa and Mauna Kea.

Lava Domes

Volcanic or lava domes are created by small masses of lava which are too viscous (thick) to flow very far. The magma from volcanic domes just pile up over and around the vent. The dome grows by expansion of the lava within and the mountain forms from material spilling off the sides of the growing dome. Lava domes can explode violently releasing a huge amount of hot rock and ash.