Volcanic Features

...igneous rocks formed by crystallisation of magma above the surface

Minor Features

Hot Springs:- if heated water is not under pressure, it won't become superheated so forms pools of water with other minerals ->Blue Lagoon, Iceland

Boiling Mud: if heated water mixes with ud, a boiling mud pool o rmud volcano is created

Fumeroles: Superheated water reaches the surface as steam above 300dc

Solfataras: Superheated water reaches the surface as steam below 300dc

Geysers: intermittent explosion og superheated water and steam at the surface caused by heating of water below the surface by volcanic activity -> Geysir, Iceland

A conduit (plumbing system) is gilled with cool, shallow water which is surface recharge or ground water. The heat source is superheated water from deep in the ground under pressure. The conduit is pressure tight due to a mineral deposit called sinter. Sinter deposits line and seal the geyser and build a cone on geyserite at the surface

1) The conduit fills with cool water and superheated water which mix. This means the pressure is released and the superheated water becomes steam

2) This cant take seconds or days. THe weight and cool temperatures of the water increase the pressure within the system and so surpress the boiling of the water

3) THe water temperature increases due to the superheated water warming the conduit which rises and condenses. Almost all the water is at its boiling point for that depth

4) If any water bubbles off at the surface, the pressure releases so the water turns into steam. This expansion causes the water to be ejected into the air

Fissure: elongated crack in the crust allows lava to spill over a large area ->Basaltic, gentle persistent lava eruptions. Found in rifts and on constructive margins ->Hekla Iceland 

Shield: lava from a vent, forms layers of less viscous lava, creating a gently sloping cone -> Basaltic, gentle, predictable/regular eruptions. Found at hot spots or oceanic-oceanic plate boundaries -> Mauna Lao, Hawaii

Acid/Dome: Very viscous lava builds up, convex cone - a plug may form -> explosive rhyolite explosions. Found on continental plate boundaries -> Puy de Domes, France

Ash Cones:- debris is ejected from crater to give steep symmetrical sides -> Andesitic, explosive. Found on destructive boundaries ->Paricuita Mexico

Calderas:- gases erupt to blast away the neck, leaving a massive crater -> Andesitic, explosive. Found on destructive boundaries -> Krakatoa, Indonesia

...Igneous rock formed by the crystallisation of magma below the surface

Lacolith:- small injections of magma form lens shapes that intrude between layers of rock, forcing overlaying strata to rch up, forming a dome ->Eildon Hills, Scottish Bolders

Batholith: deep below the surface when large masses of magma cools and solidify. As the magma cools slowly, large crystals form. They are domeshaped and may be exposed by erosion later -> Dartmoor - Hambledown Tor

Metamorphic Aureole: The area surrounding the batholith altered by heat and pressure of the intrusion

Dykes: Vertical intrusions with horizontal cooling cracks. They cut across bedding planes of rock - often in groups or Dyke Swarms -> Isle of Skye

Sills: Horizontal intrusions along the lines of bedding planes with vertical cooling cracks -> Drumadoom, Isle of Arran

Dykes and Sills are commonly made of Dolerite