GEO 110 Lecture Notes - Lecture 5: Types Of Volcanic Eruptions, Vulcanian Eruption, Strombolian Eruption
15 Jun 2018
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Lecture 5
Volcanoes & Mountain Formation
VOLCANIC ERUPTIONS
• Volcanoes are openings or vents, with or without a conical hill or mountain near them.
• There are more than 600 active volcanoes in the world.
• Volcanoes occur in the Pacific Ocean in what is called the Ring of Fire.
• Conduit fissure: magma, lava, ash and pyroclastic materials
Sursteyan eruption:
o Volcanic eruption which is categorized of series of hydro volcanic eruptions. Common in Iceland.
o A type of volcanic eruption that takes place in shallow seas and lakes.
o Represents violent explosions cause by rising basaltic or andesitic magma coming into contact with
abundant, shallow groundwater or surface water.
Eyjafjallajokull, Iceland (2010)
o Release a lot of ash material into the atmosphere. Inhibited movements/ cancelled flight or aircrafts
from Europe to North America for 5 days.
o Cauase disruption to air travel across Western and Northern Europe ove an initial period of five days.
Sulfric acid: affects respiratory system.
Magma: molten rock beneath the surface.
Plutonic rocks: Are igneous rocks that solidified from a melt at greath depth.
Extrusive rocks:
o roks that hae ee solidified ad for he aga reahes the Earth’s surfae a volcane and
cools quickly. Have small crystals.
o Magma that extrudes (force out) into crystal rocks, cools, and hardens on to the surface.
o Iniesta landforms.
Intrusive of plutonic rocks:
o which formed inside the Earth.
o Formed when magma crystallizes and solidifies underground to form intrusions
o Examples, plutons, batholits, dikes, sills, laccolits, and volcanic necks
Landform formed inside the Earth
o Batholith
▪ Massive global rock formation or a large body of igneous rock because of the intrusion and
solidification of magma. Usually consist of coarse-grained rocks, such as granite or
granodiorite.
▪ Made of inside rocks (very strong).
▪ Largest pluton form
o Dike
▪ forms a barrier, common along the coastal areas.
▪ It forms when magma intrudes into a crack then crystallizes as a sheet intrusion, either
cutting across layers of rock or through a contiguous mass of rock.
o Sill
▪ Flat intrusion of igneous rock that forms between pre-existing layers of rocks.
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Surface of the land:
o Cinder cones
o A small, cone-shaped hill usually less than 450 m high, with a truncated top formed from
cinders that accumulate during moderately explosive eruptions.
o Are made of pyroclastic material and scoria (cindery rock, full of bubbles)
o It develops from explosive eruptions of mafic and intermediate lavas.
o As the gas-charged lava is blown violently into the air, it breaks into small fragments that
solidify and fall as cinders around the vent to form a circular or oval cone.
o Volcanic or Laval dome
o Is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous
lava from a volcano.
o Are formed by relatively small, bulbous masses of lava too viscous (thick) to flow any great
distance. Commonly occur within the craters or on the flanks of large composite volcanoes
o Denudation: It is a series of geomorphic events. It involves the processes that cause the wearing
aa of the Earth’s surfae oig ater, ie, id ad aes, leadig to a redutio
in elevation and relief of landforms and of landscapes.
EATURES ASSOCIATED WITH VULCANIC ERUPTION
Composite volcanoes
• A mountain produced by a series of explosive eruptions.
• Have a crater at the summit which contains a central vent or a
clustered group of vents.
• It is formed by multiple layers of lava, ash, rock, and pyroclastics.
• Violent because of the accumulation of gases, which tends to be liquified.
• Everytime it erupts, mountain summit collapses into the magma chamber
• The essetial feature is a oduit sste hih aga fro a reseroir deep i the Earth’s rust
rises to the surface.
1. Stratovolcanoes
• The magma forming this lava is called felsic lava & cloud of hot white gases
• Charachterized by a steep profile and periodic explosive eruptions and effusive eruptions, although
some have collapsed crated called Caladera.
• They are typically steep-sided, symmetrical cones of large dimension built of alternating layers of
lava flows, volcanic ash, cinders, blocks, and bombs.
• It is built up by many layers (strata) of hardened lava, tephra, pumice, and volcanic ash
• Composite volcanoes: Mount Rainer, Washington
Magma chamber:
o A large pool of liquid roc beneath the surface of the Earth.
o The molten rock, or magma, in such a chamber is under great pressure, and, given enough time,
that pressure can gradually fracture the rock around it, creating a way for the magma to move
upward.
o The magma material is released has greater amount of silicon and aluminum
o 60-70% of silicon and aluminum material is found here
o Magma has high visocity. Any material that that is high viscosity is dense and sticky and resist flow.
Crater: a bowl-shaped or a circular surface depression, or hollowed-out area, produced by the impact of
meteorite, volcanic activity, or an explosion. It is usually found at or near the summit.
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2. Caldera “panish for kettle
• A large basin-shaped depression that forms when summit material on a volcanic mountain
collapses inward after an eruption or other loss of magma.
• May fill with rainwater to form a laje
• Deep depressions volcan Krakatoa 1883
3. Sheild Effusive volcanes
• Effusive eruptions
i. Are outpourings of low-viscosity magma that produces enormous volumes of lava
annually on the seafloor. It has low resistant flow because it is highly fluid.
ii. These eruptions flow flow directly from the asthenosphere and upple mantle, releasing
fluid magma that coolds to form a dark, balsatic rock low in silica (less than 50%) and
rich in iron and magnesium.
iii. May come from a single vent or from a flank of a volcano through a side vent.
• The shape is similar in outline to a shield of armor lyring face up on the ground and therefore it
is called shield volcano.
• Ex. Oregon and Mauna Loa (Hawaii)- Unsymettrical. Largest volcanic mountain in the world, in
terms of the area extent of its boundary.
• Basalt: a dark, fine-grained volcanic rock that sometimes displays a columnar structure. It
makes up most of the ocean floor and is the most common type of lava.
4. Hotspots volcanoes
• Plumes of upwelling basaltic
• It occurs at abnormally hot centers known as mantle plumes
• Oceanic volcanoes move away from the hot spot, they cool and subside. As continental
volcanoes move away from the hot spot, they col, subside and become extinct.
Subduction zone
• Boundaary among which the denser ocean crust is forced to move beneath less dense
continental crust.
• Convergent boundaries where at least one of the tectonic plates is an oceanic crust.
5. Hot spring & Geysers
• Occur in areas where colcanic lava lies just beneath the surface. The lava heats up water that
seeps into the Earth.
• Ground water is heated to high temperatures
• Example: Greater Yellowstone National Park
Types of Volcanic Eruptions
1. Hawaiian eruption
o The most fluid of these eruptions.
o Where lava flows from the vent in a relatively gentle, low level eruption. Lava stadily flows out
of a volcano onto the ground.
o Effusive eruptions, with basaltic magmas of low viscosity, low content of gases, and high
temperature at the vent.
2. Strombolian eruption
o Distinct bursts of fluid lava from the mouth of a maga-filled summit conduit.
o The explosions usually occur every few minutes at regular or irregular intervals.
o Associated with small lava lakes
o The explosions of lava, are caused by the bursting of large bubbles of gas, which travel upward
in the magma0filled conduit until they reach the open air.
o Scoria: are hardened chunks of bubbly lava, lava bomb
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Document Summary
Sursteyan eruption: volcanic eruption which is categorized of series of hydro volcanic eruptions. Common in iceland: a type of volcanic eruption that takes place in shallow seas and lakes, represents violent explosions cause by rising basaltic or andesitic magma coming into contact with abundant, shallow groundwater or surface water. Eyjafjallajokull, iceland (2010: release a lot of ash material into the atmosphere. Inhibited movements/ cancelled flight or aircrafts from europe to north america for 5 days: cauase disruption to air travel across western and northern europe ove an initial period of five days. Plutonic rocks: are igneous rocks that solidified from a melt at greath depth. Extrusive rocks: ro(cid:272)ks that ha(cid:448)e (cid:271)ee(cid:374) solidified a(cid:374)d for(cid:373) (cid:449)he(cid:374) (cid:373)ag(cid:373)a rea(cid:272)hes the earth"s surfa(cid:272)e a volcane and cools quickly. Have small crystals: magma that extrudes (force out) into crystal rocks, cools, and hardens on to the surface.
