vulcanicity

Question 1

what is the word volcano derived from

Answer 1

the name of the roman fire god – vulcan

Question 2

define volcano

Answer 2

tall conical structure with an opening in earth’s crust that allows molten rock from beneath the crust to reach the surface

Question 3

at what plate boundaries are volcanoes formed from

Answer 3

divergent and convergent

Question 4

difference between lava and magma

Answer 4

molten rock is called magma when it is beneath the surface
molten rock is called lava when it flows and erupts from a volcano
magma solidify to form plutonic rock such as granite and cooled slowly resulting in large crystals
lava solidify to form volcanic rocks such as basalt and cooled rapidly resulting in small crystals or glass like rock such as rhyolite

Question 5

what do volcanoes release

Answer 5

lava, gases ( sulphur dioxide ) steam, ash and rock

Question 6

define vulcanicity

Answer 6

describes the process whereby molten mantle rocks or magma flow upwards into the crust or onto earth’s surface

Question 7

define intrusive volcanic features

Answer 7

when magma rises towards the surface of the earth via lines of weakness in the crust such as faults or fractures
if they do not have communication with the earth’s surface the magma cools and solidifies in cracks and joints within the earth

Question 8

define batholith

Answer 8

very large mass of intrusive igneous rock and formed when magma cools and crystalises beneath earth
may occur when magma chamber which is a large pool of molten rock cools and solidifies
tobago batholith that crosses the island from east to west and is approximately half the size of tobago

Question 9

define sill

Answer 9

formed when magma intrudes between older rock layers and cools and solidifies along bedding planes to form usually horizontal sheet of igneous rock
do not cut across pre existing rocks

Question 10

define dyke

Answer 10

formed when magma moving upward towards surface cuts across pre existing bedding planes and cools and solidifies to form an usually vertically igneous rock
large number of dykes called dyke swarm can occur together in an area
thickness can vary from a few centemetres to many metres
moule a chique headland located in southern tip of st lucia
pakarina mount in guyana

Question 11

define laccolith

Answer 11

formed when pressure of magma intruding between rock layers forces overlaying rock strata to bulge upwards to form dome umbrella shaped igneous rock feature
igneous intrusion injected between two layers of sedimentary rock
tend to form at relatively shallow depths and typically formed by relatively viscous magmas
cooling takes place slowly undergroundn resulting in large crystals
over time surface rocks above laccoliths erode away completely exposing core mound of igneous rock

Question 12

explain viscosity of magma

Answer 12

depends on silica content and temperature
fluid magma of low viscosity has lower silica content and is usually of a higher temperature than thick viscous magma
due to silica content lava can also be described as being basic or acidic

Question 13

define basic lava

Answer 13

rich in iron and magnesium
low in silica
very hot 1000-1200
runny fluid non viscous
flows for a very long time before solidifying
gentle eruptions
basalt common rock formed from basic lava
form shield volcanoes
Mauna Loa in Hawaii

Question 14

define acidic lava

Answer 14

rich in silica
not as hot 800 to 1000
slow moving viscous - thick and sticky
solidifies quickly on contact w air because not as hot
does not flow for long distances
violent eruptions has to push through with a lot of force
granite common rock formed from acid lava
forms dome volcanoes
Pitons in St Lucia

Question 15

define dome volcno

Answer 15

formed by acid lava – cools and solidifies quickly
forming high steep sided volcanoes which convex sloped and narrow bases

Question 16

define shield volcano

Answer 16

formed by basic laval which is runny or more fluid and so spreads over a wide area before solidifying
found on constructive plate margins
typically gentle eruptions and non explosive
produces low flatter volcanoes with gentle slopes and wide base
not as hot as acid lava thus solidifies faster on contact with air

Question 17

define composite/ stratovolcano

Answer 17

steep sided cone compound of alternate layers of acid lava and ash
found on destructive plate margin explosive eruptions
development of cone begins with violent eruptions ejecting ash and cinders which settle around vent
this eruption clears vent allowing lava to flow out fairly easily
lava buries ash and cinders and eventually the trapping of gases lead to a violent eruption which will once again clear the vent thus repeated eruptions of ash and cinders
followed by free lava flow builds composite volcanoes

Question 18

define ash and cinder cone volcano

Answer 18

formed from ash and magma cinders
magma cinders partly burned solid pieces of magma that fall to ground following volcanic eruption
eruption contains little lava as magma hardens and breaks up into pieces during eruptions
as a result cinder cone volcanoes tend to be smaller

Question 19

define extrusive volcanic features

Answer 19

magma reaches the surface of the earth either through a long crack also termed a fissure or a vent
volcano and lava plateau

Question 20

define lava plateau

Answer 20

sometimes large quantities of basic lava slowly spill onto earth’s surface from fissures
these fissures eruptions can cause basic lava to spread out over very wide area before cooling and solidifying over time
over time a number of fissure eruptions in same area can lead to a high or elevated area that is fairly level or flat
also known as basalt plateau
deccan plateau india 650 000 km square covered

Question 21

define pyroclastic flows

Answer 21

dense super heated fast moving mixture of volcanic ash rock fragments (soldified rock pieces) and gases
can be more than 800 degrees c and moves at speed of up to 700 km h
burns everything in its path like houses and buildings agricultural land
usually occur during explosive eruptions from composite volcanoes

Question 22

define mudflows and lahar

Answer 22

mixture of water and rock fragments flowing quickly down slopes of volcanoes
can be created when significant rainfall event like a hurricane or storm or melt water from glaciers and snow mix with volcanic ash
forms a thick slurry that flows quickly down flanks of volcano covering everything in its path
1985 nevado del rees columbia

Question 23

list 6 other hazards of volcanoes

Answer 23

destruction of property – hawaii
volcanic blasts – large amount of energy is suddenly released directed upward into the atmosphere – 1980 mt st helens killing 34 triggered huge floods and mudflows
emissions of toxic fumes – co2 is commonly emitted during eruptions can be lethal as it suffocates humans and animals – sourfriere hills volcano montserrat and 1986 cameroon west africa 1746 killed from volcanic gases
ash – lingering in air from volcanic eruption can cause inflammation of lungs leading to pneumonia and even death and respiratory illnesses– mount pinatubo philippines 1991
tsunamis – explosive eruptions in the sea can create huge sea waves can cause flooding and even inundate entire coastal communities
pollution and effects on environment - sulphur dioxide emitted from eruptions increase problem of acid rain which pollutes atmosphere and rivers and lakes – mt pinatubi 1991

Question 24

explain how fertile soil is a benefit of volcanoe

Answer 24

warm and wet conditions make weathering of volcanic material even more favourable enabling its quick decomposition to form fertile soils

Question 25

explain how tourism is a benefit of volcanoes

Answer 25

volcanoes provide beautiful scenery which can boost tourism
grand etang crater lake grenada
st pitons st lucia
hot springs – regions where water seeps between rocks in volcanic regions and get heated to temperatures above 100
as water flows back to earths surface quietly and continuously and forms hotsprings
rich in dissolves minerals and is of therapeutic value
geysers heated water and underground steam is ejected out of vent with a great force this jet of water and steam rises to great heights and then subsides old faithful geyser in yellow stone park usa ejects water at 45m h every hour

Question 26

explain how geothermal energy is a benefit of volcanoes

Answer 26

harnessed from heat given out by volcano then used to produce electrcity for a number of uses
groundwater heated by hot rocks underground to give off steam which is then tapped to generate electricity

Question 27

explain how minerals is a benefit of volcanoes

Answer 27

metals gold silver copper
gemstones sapphire opal found in igneous rock
gemstones allows for development of mining industries around regions of volcanic activity providing jobs for locals and bring about industrials development