Minor Forms of extrusive activity

Low pressure outlets of steam and gas

• Associated with active and dormant volcanoes.
• Steam, carbon dioxide, carbon monoxide, hydrochloric acid- all released.
• Sulfur can also be released, when this happens it becomes as SOLFATERA.

Solfatera

• A fumerole that contains sulfur. For example Lake Nyos, Bay of Naples Italy.

• Ground water source flows close to area of recent intrusive activity, water is heated.
• Temperatures vary between 20-90oc.
• Often have high mineral content because hot water dissolves a lot of solids.

• Type of hot spring, hot water and steam are ejected from the surface in a fountain.
• They are found in areas of intense volcanic activity.

1) Water is heated to above boiling point by magma deep in the crust.

2) Water is pressurised, forces its way to surface along cracks.

3) Hot water and steam spray out from vent.

• They erupt periodically- only erupt when pressure has built enough to force water out.

For example, Old Faithful, Yellowstone National Park USA.

• Type of hot spring.
• Form in areas of very fine grained soil, such as ash and clay
• Water and mud mix to form a mud pool
• Can contain brightly coloured mud- minerals (iron, sulfur) can produce purple, orange and yellow mud.

An example of a boiling mud pool is Yellowstone National Park, USA. They are also found in Iceland.