Chapter 3 Glossary
Viscosity
A measure of how easily a substance flows. The more viscous a substance, the less
readily it flows. clickable link with table of viscosities? do same for heat capacity
Lava
Molten rock that spills out onto the Earth’s surface. Molten rock that does not reach the
Earth’s surface is referred to as ‘magma’.
Magma
Molten rock material beneath the Earth’s surface. Molten rock that reaches the Earth’s
surface is referred to as ‘lava’.
Plate tectonics
Unifying theory of the Earth Sciences, involving tectonics as a global system, in which
the crust is divided into many different plates. This theory strives to explain earthquakes,
volcanism, sedimentary deposits, economic mineral deposits, and many other aspects of
geology. It is still being refined.
Glowing clouds
Also known as ‘nuée ardentée’ or ‘pyroclastic flows’. An avalanche of very hot volcanic
gases and volcanic ash, moving at a very fast speed.
photo
Lahar
A mudflow composed of unconsolidated volcanic debris and water.
photo or video
Tsunami
Giant, long-period sea waves caused by oceanic disturbances, such as fault movements,
volcanic eruptions, meteorite impacts, and landslides. (Abbott)
photo or video
Olivine
Common magnesium iron silicate mineral ((Mg,Fe)2SiO4), often found in dark-coloured
igneous rocks. It is a primary mineral in the upper mantle, and basaltic magmas, but can
also be found in some moon rocks and meteorites.Green to yellow-green in colour.
photo olivine (2), photo basalt
Quartz
Silicate mineral (SiO2) that is highly resistant to weathering. Quartz is found in lightcoloured igneous rocks, as well as many sedimentary and metamorphic rocks. There are
many colour variations, depending on what elements are substituted into the structure, eg.
amethyst is a form of quartz.
Basalt
A dark, finely crystalline volcanic rock typical of low-viscosity oceanic lavas. (Abbot,
glossary)
Rhyolite
Volcanic rock made of feldspar, ferromagnesian and quartz minerals, and a very high
silica content. It is associated with very violent volcanic explosions.
Hot-spots see chap 2
Geographic location where a plume of magma has risen from the mantle, and penetrated
through a plate to reach the surface of the Earth.
Shield volcanoes
These are the largest types of volcanoes, but they are very gently arching. Eruptions are
usually non-explosive, and consist of low silica content magmas. eg. Mauna Loa
J.D. Griggs, www.usgs.gov
Mauna Loa
www.usgs.gov
Volcanic vent
Opening in the Earth’s crust that allows the escape of volcanic gases and molten rock.
They may be in the form of cracks, holes or longer fractures.
http://www.decadevolcano.net/photos/indonesia/bromo_40807.jpg
Steaming vent inside the crater of Bromo volcano, Indonesia.
photo of fissure
Mauna Loa, usgs
Phreatic eruption
An explosion of steam, water and ash resulting from the contact of hot lava or magma
with water (either ground or surface). They generally do not involve molten lava.
www.usgs.gov MSH
Subduction zone get from chap 2
Convergence of tectonic plates. At this point, one plate is forced underneath the other.
(Keller, glossary)
Pyroxene prev ch
A group of important rock-forming silicate minerals of variable composition, among
which calcium-, magnesium-, and iron-rich varieties predominate.
"pyroxene." Britannica Concise Encyclopedia. 2004. Encyclopædia Britannica Premium Service.
20 Sept. 2004 <http://www.britannica.com/ebc/article?tocId=9376205>.
Plagioclase prev ch
Type of feldspar (framework silicate) that ranges from sodium to calcium rich. The
chemical formula is (Na,Ca)Al(Si,Al)Si2O8.
Stratovolcano prev ch
Steep-sided, symmetrical volcanoes that often produce andesitic or rhyolitic magmas.
This type of volcano is layered in composition because of alternating lava and
pyroclastics. Mount Fuji is an example of a strato-volcano.
http://gojapan.about.com/od/japanpicture1/l/blnat_tanofuji7.htm
www.usgs.gov
Resurgent caldera eruptions
no clue? Toba good maps, find photo
Volcanic Explosivity Index (VEI)
Logarithmic scale for ranking volcanic eruptions in terms of their severity.
Richter Scale
Quantitative, logarithmic scheme for describing the magnitude of an earthquake.
Welded tuff
Rock composed of fused volcanic ash and volcanic debris. The rocks forms a solid mass
because the glowing cloud particles are so hot when they settle that they fuse together.
This photograph is likely a volcanic agglomerate, formed with slightly larger particles
than a conventional welded tuff.
photo D. Velasco
http://www.casdn.neu.edu/~geology/department/staff/colgan/iceland/husafell/dv012.htm
Crater lake
A lake that normally results when a volcanic caldera fills with surface water. Less
commonly, meteorite impacts may cause crater lakes as well.
http://volcano.und.nodak.edu/vwdocs/volc_images/north_america/crater_lake.html
northern quebec
http://photojournal.jpl.nasa.gov/jpeg/PIA03434.jpg
Caldera
Calderas form when volcanoes collapse, leaving behind massive circular or quasi-circular
holes. This generally results from the emptying of the underlying magma chamber, which
is supporting the volcano. The ground can no longer withstand the mass above it, and
subsides. The collapse may occur in stages, or all at once.
Tephra
Term that encompasses all of the different types of unconsolidated material that may be
ejected from a volcano, including (from largest to smallest) volcanic bombs, blocks,
cinders, and ash.
Angle of repose
Natural angle that forms between the horizontal at the top of a pile of unconsolidated
material, and the sides. Materials may vary slightly in their angles of repose.
diagram
Tuff
Rock that forms when volcanic ash gets wet, and becomes cemented.
Volcanic bombs
Pieces of lava larger than a few centimetres in diameter that are thrown into the air during
an eruption. They cool into solid fragments before they reach the ground. (Wikipedia)
basaltic bombs Mauna Kea www.usgs.gov
http://www.gc.maricopa.edu/earthsci/imagearchive/bombs.htm
photo- steve’s
Fossilized people
Fumarole
Natural volcanic vent that allows for the escape of gasses. They form on the flanks of
active volcanoes.
www.usgs.gov
sulphur gas escaping from fumarole at Kilauea.
http://helios.bto.ed.ac.uk/bto/microbes/yellow.htm
thermal vent in Yellowstone National Park
Fluorosis
Normally a relatively benign condition resulting from an excessive intake of fluorine,
resulting in the discolouration of teeth. However extreme cases causing death may result
from venting of fluorine-rich volcanic gases.
Jokaulhlaups
High energy floods resulting when a volcano erupts beneath a glacier, producing a lot of
meltwater and steam. The glacier prevents meltwater from escaping until sufficient
pressure has built-up to lift the glacier ice. At this point, a high energy flood results.
http://www.hi.is/~mmh/gos/photos3.html
Ice-age
Period in time where temperatures are lower than they are presently, resulting in
expansion of polar and alpine ice into more temperate regions. We are currently in an
‘interglacial period’, as opposed to an ice age.
Volcanic winter
A global drop in temperature resulting from volcanic ejecta (ash and/or aerosols) in the
atmosphere, which blocks solar radiation. It may last a few years. In fact, there are
indications in the fossil records that volcanic winters may have caused mass extinctions.
horrific artistic rendition
Pyroclastic
Volcanoes eject solids, liquids and gasses. Pyroclastic is the term referring to the solid
materials resulting from explosive volcanoes. Particle sizes can range from very fine ash,
to larger pieces of debris.
Radiometric dating
Predicting the age of materials based on the decay rates of naturally occurring isotopes,
and the abundance at which they occur in the present.
Seismographs
Instrument used to record the size of the vibrations that result from tectonic movements
of the Earth. Produces a seismogram, which is a drawing of the waves representing
relative magnitude of the movements over time. The Richter Scale is based on the
amplitude of the waves produced on the seismograph.
photo
Volcanic tremors
Seismic activity marking the beginning of magma movement under a volcano. This
shaking starts before a volcano erupts, and continues through the eruption. It feels more
like standing next to a train than a violent shaking (taken directly from course
manual....add more?)
Global Positioning System (GPS)
Satellite navigation system that can determine a person’s precise location almost
anywhere on Earth, or in Earth’s orbit. Elevation and position can be determined within
centimetres using state-of-the-art equipment.
Infrared
Infrared radiation falls between visible light and microwaves on the electromagnetic
spectrum. The term means “below red” (infra is “below” in Latin) because red is the
longest wavelength in the visible portion of the spectrum. Infrared radiation has
wavelengths between 700nm and 1mm. Infrared is felt as sensible heat.
http://science.nasa.gov/newhome/help/glossfig1.htm
Curie point
Temperature threshold above which a material loses its magnetic characteristics.
Andesite
Volcanic rock named after the Andes Mountain range of South America having an
intermediate silica content. Contains feldspars, iron and magnesium rich silicates, but no
quartz.
Magnetite
Magnetic mineral that is formed either biogenically or chemically. Major source of iron,
as it is composed of Fe3O4.
photo with magnet
P waves
P (primary) wave – “first seismic wave to reach a seismometer. Movement is by
alternating push-pull pulses that travel through solid, liquid, and gas” (Abbott, glossary)
video in ch. 1...if you can save it.
S waves
S (secondary) wave – “second seismic wave to arrive at the seismometer. Movement
occurs by shearing particles at right angles to travel path. S waves move through solids
only” (Abbot, glossary)
Rockslide
???? leave until slope failure chapter is finished
Silicate minerals prev ch
A type of mineral made of oxygen and silicon. Silicates are grouped based on their
molecular structures, and make up most of the Earth’s crust. Quartz (SiO2) is a common
example of a silicate mineral.
Stratosphere
The stable atmospheric layer above the troposphere. (see Unit 1)