Ascension Island Volcanology

Menu

Skip to content
  • Home
  • About the project
  • Project News
  • People
    • Jenni Barclay
    • Richard Brown
    • Katy Chamberlain
    • Ben Cohen
    • Anna Hicks
    • Sue Loughlin
    • Darren Mark
    • Katie Preece
    • Fin Stuart
    • Charlotte Vye-Brown
    • Jon Davidson
    • Bridie Davies
    • Jane Scarrow
    • Rebecca Winstanley
  • The geology of Ascension Island
  • Related Links and Further Reading
    • Partner Sites
    • Publications
    • Request more….

Request more….

Can’t find the resource you’re looking for?

Contact us at: ascensionvolcanology@gmail.com

 

Share this:

  • Click to share on X (Opens in new window) X
  • Click to share on Facebook (Opens in new window) Facebook
Like Loading...

Geology Word Bank

Felsic Rocks: Igneous rocks that contain >65% silica (SiO2), common minerals include quartz and alkali-feldspar. Rich in Si, Al, K and Na and light in colour they are less dense and more viscous than their mafic equivalents.

Mafic Rocks: Igneous rocks containing ~59% silica, common minerals include olivine, pyroxene and plagioclase feldspar. Rich in Fe, Mg and Ca they are dark in colour and denser and less viscous than their felsic equivalents.

Mantle Plume: An upwelling of abnormally hot molten rock from within the mantle of the Earth. Plumes are often used to explain volcanic activity away from a tectonic plate boundary e.g. Hawaii.

Fractional Crystallisation: The process by which different minerals crystallise out of a body of molten rock (magma) as it cools. Fe and Mg-rich minerals crystallise first (high temperature) leaving progressively more Si-rich melt behind.

Pyroclastic Density Current: A flow of hot ash, rock and gas that forms when the ash column produced by an explosive volcanic eruption

Pumice: A felsic volcanic rock which is light in colour and has an extremely low density due a high abundance of small bubbles in the rock structure. Bubbles represent gasses trapped in the magma during eruption due to the high viscosity of felsic melts.

Scoria: A mafic volcanic rock which is dark in colour and contains a high proportion of bubbles. Formed during explosive eruptions of mafic magma scoria is more dense than pumice due to its Fe and Mg-rich compostion.

Vesicles/Vesicularity: Vesicles are voids in a volcanic rock that resulting from gas bubbles forming within a magma while it is molten. When the magma is erupted it cools rapidly and the edges of the bubbles are frozen in place. Vesicularity of a rock is what % of a rocks volume is taken up by vesicles.

Xenolith: A chunk of rock found within an igneous body (lava flow, pyroclastic density current, or plutonic body) that has a different origin to the surrounding igneous rock. Usually representing the rocks through which the molten material travelled to reach the surface.

Contact us:

If you have any questions please feel free to tweet or message us @AscensionVolc

 

 

 

 

 

 

 

 

Blog at WordPress.com.
  • Subscribe Subscribed
    • Ascension Island Volcanology
    • Already have a WordPress.com account? Log in now.
    • Ascension Island Volcanology
    • Subscribe Subscribed
    • Sign up
    • Log in
    • Copy shortlink
    • Report this content
    • View post in Reader
    • Manage subscriptions
    • Collapse this bar
%d