Pyroclastic:Adjective used to describe rock material formed by a volcanic explosion.
Pyroclastic Flow:Mixtures of hot gas and ash travelling very quickly down the slope of a volcano.
Ring of Fire:The belt of volcanoes that surround the Pacific Ocean. This belt contains about two-thirds of the world's active volcanoes.
It is marked by the volcanic chains of Japan, Kamchatka, South Alaska, the Aleutian Islands, the Cascade Range of the US and Canada, Central America,
the Andes, New Zealand, Tonga, Vanuatu, Papua- New Guinea, Indonesia, the Philippines, and last but not least
the Mariana, Izu and Bonin Islands which complete the circle.
Seafloor spreading:The process in which the ocean floor is extended when two plates move apart.
Seismograph:An instrument that is used to record vibrations of the Earth.
Shield Volcano:Volcano which has a broad shaped cone with gently slopes. Shield volcanoes are built by runny lava flows.
Silica:Fundamental component of volcanic rocks. It is the most important factor
determining the fluidity of magma. The higher the silica of a magma the greater its viscosity.
Solfatara:Italian word used to describe a fumarole that emits sulphurous gases.
Spatter:Lava fragments, between 64mm and 30cm in size. which are often emitted as hot clots. Spatter often welds together
to form steep-sided cones.
Spatter cone:Steep-sided cone of spatter.
Stratosphere:The upper layer of the atmosphere.
Stratovolcano:See composite volcano.
Strombolian Eruption: Short-lived eruptions that throw out blocks and bombs. Lava flows also occur.
Subduction:The process in which one plate is pushed downward beneath another plate
into the underlying mantle when plates move towards eachother.
Tephra:Collective noun for all sorts of volcanic material that are erupted from a crater or vent.
Tremor:Earthquake activity with a low amplitude associated with the movement of magma.
Tsunami:Japanese word that is used to describe huge sea-waves generated by earthquakes or violent volcanic eruptions.
Tuff Cone:Steep conical hill with a deep, wide crater. The cone is composed of thin layers of fine fragments.
A tuff cone is smaller and steeper than a tuff ring.
Tuff Ring:A broad, circular, low-rimmed, well-bedded accumulation of fine fragments, often 1km in diameter, around a crater.
The crater of a tuff ring is wider than the one of a cinder cone.
Vent:The vent is an opening at the Earth's surface through which volcanic materials are released.
Viscosity:Term to show how sticky a magma or lava is.
Volcanic Ash:Volcanic rock which is exploded from a vent in fragments less than 2mm in size.
Ash may be solid or molten when first erupted.
Volcanic Gas:Volcanic gas is contained within magma. As the magma rises to the Earth's surface
the gases are exsolved and can become a very important factor in the violence of an eruption.
Because some gases are toxic they can suffocate people. Examples of volcanic gases include steam, sulphur dioxide and carbon dioxide.
Volcano:A cone which is formed above and around a vent by accumulations of erupted volcanic
materials like ash, pumice,lava flows and other volcanic rocks. "Volcano" can refer to both the vent and the cone.
Volcanologist:A person who studies volcanoes and their behaviour.
Volcanology:The science of volcanoes.
Vulcan:God of fire of the ancient Romans. The volcano is named after Vulcan.
Vulcanian Eruption:A Vulcanian Eruption is similiar to hydrovolcanic activity.
Much gas as well as ash, cinders and pumice are given off.