Volcanos Flashcards
What are the four principal types of Volcano
Cinder Cone
Shield
Composite
Dome
What kind of lava conditions are likely to lead to fire fountains
Low silica content, but lots of gas
One of the most spectacular fire fountaining events ever recorded on Kilauea produced a lava spray 580 m high at the Kilauea Iki vent in 1959.
What type of lava conditions lead to shield volcanos
Where are they usually found
What is the name for their typical eruption type
Low silica - therefore low viscosity
Shield volcanoes are usually found at constructive (where plates move apart) or tensional boundaries.
Eruption type is Hawaiian
Hawaiian eruptions are the calmest of the eruption types. They are characterized by the effusive emission of highly fluid basalt lavas with low gas contents. The relative volume of ejected pyroclastic material is less than that of all other eruption types. The hallmark of Hawaiian eruptions is steady lava fountaining and the production of thin lava flows that eventually build up into large, broad shield volcanoes.
What kind of lava conditions lead to Dome Volcanos
Highly viscous, silica rich, low temperature, low gas (so not explosive)
It solidifies shortly after leaving the vent
Why do composite volcanos have that name
Where are they usually found
They are made of alternating layers of lava and ash (in constrast to others made of just lava)
They are usually found at destructive (where two plates are moving towards each other) or compressional boundaries.
What is a pyroclastic flow
A pyroclastic flow is a mixture of hot steam, ash, rock and dust.
A pyroclastic flow can roll down the sides of a volcano at very high speeds and with temperatures of over 400°C.
What volume of material needs to be emitted to count as a supervolcano
What amount is typical of a large volcano
1,000km3
c.f.
1 km3 for a typical large volcano
How wide is the supervolcano caldera at Yellowstone Park
55 by 80 km
In what year was the population of Montserrat evacuated (how many people)
When were the most intense eruptions
11,000 in 1995
The most intense eruptions were in 1997
Despite the evacuations, 19 people were killed by the eruptions as a small group of people chose to stay behind to watch over their crops.
What is the name for a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water.
From where does the term come
What is particularly good at creating these flows any why
For kudos, what conditions have created the biggest of these flows
Lahar
It is an Indonesian term
Pyroclastic flows are particularly efficient at generating lahars because they have the capability to melt large quantities of snow and ice in a just few hours.
Lahars can also be generated by the basal melting of glaciers by lava flows. Basal melting of glacial ice in Iceland has produced largest historic lahars, in terms of discharge. These water-rich, glacial outburst floods are called jokulhlaups.
What are Cinder Cones properly known as
What eruption type are they associated with
Scoria cones
Strombolian eruptions (although Mafic stratovolcanoes can also do Strombolian eruptions)
(Strombolian eruptions are named from the small volcano-island of Stromboli (image), located between Sicily and Italy. This volcano has been erupting almost constantly for hundreds of years. It erupts irregularly every twenty minutes or so to produce an episodic lightshow that gives rise to its nickname, the “Lighthouse of the Mediterranean”.)
Strombolian activity is characterized by short-lived, explosive outbursts of pasty lava ejected a few tens or hundreds of meters into the air. Unlike Hawaiian eruptions, Strombolian eruptions never develop a sustained eruption column.
What are the most common type of volcano (and incidentally, the smallest with heights typically less than 300m)
Cinder Cone
How are ‘fire fragments’ better known
What is the Greek name for ash
What is the name used for in modern terminology
Pyroclasts
Tephra (actually its the generic term for any airborne pyroclastic accumulation)
What are the three types of pyroclasts (and what are their size scales)
Ash (very fine <2mm)
Lapilli (pea to walnut size 2- 64mm) aka cinders
Blocks and bombs (>64mm)
What are the two types of pyroclastic flow
NUÉE ARDENTES – these contain dense lava fragments derived from the collapse of a growing lava dome or dome flow
PUMICE FLOWS – these contain vesiculated, low-density pumice derived from the collapse of an eruption column.
Who came up with the name nuee ardente
What does it mean
And what inspired the name
French geologist Alfred Lacroix
It means glowing cloud
He used it to describe the pyroclastic flow at Mt Pelee in 1902.
What and When was the last Supervolcano to erupt
Toba, Indonesia 74,000 years ago
What type of lava compositions are less fluid
andesitic to rhyolitic lavas
which have high silica content
Because they are less fluid they are most likely to trap gases (o - oh)
What type of Basaltic lava is smooth or ropy
What type of lava has fragmented surfaces, rough and spiny with a ‘cindery’ appearance
Which is likely to erupt first from a vent
Pahoehoe (pron. Pa - hoy hoy) lava
and
A’a (pron. ah ah) lava
Pahoehoe is typically erupted first
Pahoehoe is often converted to a’a as lava advances downslope, away from the volcano. (The pahoehoe-to-a’a conversion can be caused by either an increase in flow viscosity, or an increase in the rate of shear.)
What type of lava does andesite generally produce
Blocky lava
Its blocky because of the higher viscosity
With high silica rich lavas, volcanos tend to explode.
But.. degassed they can release lava, which being viscous doesn’t flow too far from the vent
What kind of structures are created (name the two key ones)
Lava domes
and/or, if there is asymetric flow down one side, the vent can produce an elongated extrusion called called a coulée or a dome flow.
How else are composite volcanoes known
What is the average composition overall of composite volcanoes
Stratovolcanoes
Andesitic (although many oceanic stratovolcanoes tend to be more mafic than their continental counterparts.)
What is the name for vent openings that allow the escape of volcanic gases
Fumaroles
What famous volcano was the first instance of a volcano being created from nothing, to the point of its extinction at a height of 424m
Where is it
Paricutin,
200 miles west of Mexico City
Three weeks before the Paricutin eruption occurred, the people near Paricutin village heard the rumbling noises that resembled thunder, yet they were confused because the skies were clear of clouds. The noises were associated with earthquakes at depth near Paricutin. On February 20, 1943 a farmer, Dionisio Pulido, and his wife were burning shrubbery in their cornfield when they observed the earth in front of them swell upward and crack to form a fissure 2-2.5 m across
Strombolian pyroclastic activity began at the site the following day and by the end of the day it generated a 40-m-high scoria cone. In one week it grew to a height of 100 m from the accumulation of bombs and lapilli, and it was raining down finer fragments that burned and eventually covered the village of Paricutin. The eruption was unusually long for a strombolian eruption, with several eruptive phases occurring over a 9-year period. After about two years of mostly pyroclastic activity the pyroclastic phase began to wane, and the outpouring of lava from the base of the cone became the dominant mode of eruption over the next 7 years. The eruption ceased in 1952. The final height of the scoria cone was 424 m.
