Volcano related terms.

A

• ʻAʻā : Type of Lava flows with extremely rough and irregular surfaces.
  
• Active volcano : A volcano that is currently erupting, one that has erupted during recorded history and is likely to erupt again.
• Ash : Fine particles of pulverized rock (tephra) erupted from the vent of a volcano. Particles smaller than 2 mm in diameter.

B

• Ballistics or volcanic bombs : An explosively ejected rock fragment from a volcanic vent in any direction. Tephra particles larger than 64 mm in diameter.
  
• Basalt :  A dark colored volcanic rock with low silica content.
  

C

• Caldera : An volcanic depression formed by the collapse of the ground above the magma chamber, which empties during very large volcanic eruption. It's diameter is many be times larger than the size of the individual vents, such as the "Ambrym caldera".
  
• Crater :  A bowl or funnel shapped depression at the top of the volcanic cone which formed by either explosions or collapse at the vicinity of the volcanic vent, such as "Ambrym and Yasur craters".
• Cinder cone : A small conical-shaped volcano formed around the volcanic vent by a accumulation of ejected ash, tephra and others volcanic debris such as "Lopevi cone".
  

D

• Dormant volcano : A volcano that is not currently erupting, but is tought to be likely to erupt in the futur.

E

• Earthquake : A sudden motion or trembling in the crust caused by the abrupt release of accumulated stress along a fault. Different types of earthquakes or seismicity include low frequency, high frequency (or ‘volcano tectonic’ earthquakes) and hybrid earthquakes; and tremor. Earthquakes can occur in swarms, where the largest magnitude earthquakes are all of a similar size.
  
• Eruption : The expulsion of volcanic material such as the effusion of lava, volcanic gases from a volcanic vent or fissure at the earth's surface.
  
• Eruption hazards : Depending from the eruption style, and may include explosions, ballistic or volcanic bombs, lava flow, ash, landslide, volcanic gases, lighting, lahars or mud flow, pyroclastic flow, tsunami and/or earthquake.
• Eruption plume : A volcanic ash cloud emitted from a volcanic vent or volcano.
• Explosions : Rapid increase in volume and release of energy in an extreme manner with generation of hight temperature and release volcanic materials such as ejection of ballistics or volcanic bombs, gases and steam from the vent.
• Extinct volcano : A volcano that is not presently erupting and is inlikely to do so in the futur.

F

• Fissure : A large crack in the ground allowing magma to travel up and erupt onto the surface.

H

• Hot spring : A surface feature of a geothermal system, where warm or hot water flows out of the ground.

L

• Lahars or mud flow : A volcanic mudflow – a flow of water-saturated, typically dense volcanic material that resembles a flow of wet concrete and usually flow down topographical lows (i.e. valleys) and can travel well over 100 km from the source, and can be dangerous to downstream populations who are unaware of the approaching hazard.
  
• Lapilli : A small stony particle ejected from a volcano.
• Lava : A molten rock that has reached the Earth's surface and been thrown out of or has flowed from a volcano or volcanic vent.
• Lava dome : A steep-sided pile of viscous (i.e. sticky) lava at a volcanic vent. The surface is often rough and blocky as a result of fragmentation of the cooler outer crust during growth of the dome. Lava domes can collapse and cause block and ash flows.
• Lava flow : An outpouring of lava from a vent or fissure that spreads along the ground surface.
• Lava fountain : A pillar-like jet of lava that can reach heights of tens to hundreds of meters above a volcanic vent. Some lava fountains erupt from long fissures. Lava fountains are a common feature of basaltic eruptions; forming scoria deposits and feeding lava flows.
  
• Lava lake : A volcanic lake that usually contained a large  volume of liquid lava inside the crater.

M

• Maar : A volcanic crater formed by a phreatic or phreatomagmatic eruption. Typically the eruption occurs in a wet or low lying area. These craters are often wide, but shallow.
  
• Magma : Molten or partly molten rock beneath the surface of the earth.

P

• Pahoehoe : Type of lava flows with a smooth, continuous surfaces.
  
• Pumice : A very light and porous solidifed fragment of volcanic rock that forms during explosive eruptions.
  
• Pyroclastic flow : Fast-moving, lethal, hot clouds of ash, rocks and gas, caused by a volcanic eruption, moving laterally  and usually down topographical lows (i.e. valleys) at high speeds (usually between 40 to 100 km per hour). They can travel a few hundreds of metres to kilometres from the source.

S

• Scoria : A solidified fragment of volcanic rock containing gas bulles. Often a black or red colour.
  
• Silica : Another name for silicon dioxide, the basic building block of volcanic rocks. Silica is a major constituent of most magmas and the amount of silica controls the viscosity of the magma: the greater the amount of silica, the higher the viscosity of the magma.

U

• Unrest : Prior to an eruption, volcanoes are said to be in state of volcanic unrest when magma or its associated fluids are interacting with country rock, groundwater or hydrothermal fluids to produce noticeable signs.
  
  

V

• Vent : The opening at the earth's surface through which volcanic materials are erupted, or were erupted in the past.
• Viscosity : A measure of the resistance for a liquid to flow .
  
• Volcanic alert level : A system that defines the current level of activity at Vanuatu's active volcanoes.
• Volcanic gases : Deep magma in the earth contains dissolved gases. As the magma rises closer to the ground surface, these gases are released and, because they are so mobile when compared to the sluggish liquid magma, they rise to the surface and are discharged through vents, fumaroles, and the soil. There are many types of volcanic gases, with the most common being water vapour (H₂O); sulphur as sulphur dioxide (SO₂) or hydrogen sulfide (H₂S); nitrogen, argon, helium, methane, carbon monoxide and hydrogen. Many of these are poisonous or cause asphyxiation.
  
• Volcano : A vent or opening in Earth's surface through which magma and associated gases erupt, and the form or structure that is produced by the deposits or the eruption process.
  
• Volcanology : The study of volcanoes.