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Flashcards in Volcanoes Deck (48):
1

Whats a fissure eruption

2 plates moving apart + lava being injected THROUGH FISSURES rather than through a central vent

The Basalt can form a LARGE PLATEAU - fill in the hollows left as the plates spread

(Giant's Causeway in Ireland are part of Lava Plateau when N.American + Eurasian plates moved apart

2

Types of Volcano

Shield
Composite Cone
Ash and Cinder Cone
Acid/dome

3

Shield Volcano

-Not a lot of explosive activity
-Shape of the volcano is dependent on the TYPE OF LAVA
^^^^^^^^ basic lava = very fluid = wide volcano with shallow slopes
^^^^^^^^ acidic and viscous lava = steeper and convex sides > <

(Mauna Loa - 9750m high + 500km in diameter)

4

Composite Volcano

THE MOST COMMON TYPE

-Formed by alternate eruptions + layers of ash + lava
-Large explosions cab blow the top of the cone off - develop into a crater
-Parasitic side cones often develop non the FLANKS OF THE VOLCANO

(Mt Etna + Mt St Helens)

5

Acid / dome volcano

-Acid lava quickly solidifying when it erupts
= Steep convex cone shaped volcanoes produced
^^^^ as lava cools near the crater

(Mt Pelee)

6

Ash and Cinder Cone Volcano

-Formed from Ash, Cinders and Lava (ejected from a central vent)
-Steep and Symmetrical sides

(Mt Paracutin, Mexico)

7

Whats the Caldera

-From a build up of gases that can causes extremely violent eruptions - can remove the whole summit of the cone
-Crater formed when the sides of the cone subsidise (forms several km in diameter)

(Santorini + Yellowstone Volcano)

8

What are Mantle Plumes

-Caused by intensive radioactivity in the Earth's Core
-Create a huge column of magma - called a 'Plume'

1. the rising mantle plume is stationary (HOTSPOT)
2. the tectonic plate (oceanic) moves over the hot spot and an active volcano is on top
3. active volcano > eroded volcanic islands > sea mounds (dropping below sea level)

9

whats an Intra-plate Volcano

occurs with the plate and not the edge

due to mantle plumes (hotspots)

10

Basic Lava

more Basaltic

more Silica = more viscous (basic lava has low viscosity + low silica content)

1200*C degree heat and is runny (FAST)

takes a long time to cool and solidify

eruptions are frequent but not explosive

ejects lava + steam

at CONSTRUCTIVE MARGINS as magma rises from the mantle

mobile as it retains its gas content

11

Acid Lava

more Andesitic

more Silica = more viscous and high silica content

less hot 800*C degree heat

flows slowly and over a shorter distance

cools ans solidifies quickly when fl,owing over short distances

loses gases quickly

ejects ash, rocks, gases, steam, lava

less frequent eruptions but are more violent -gas build up

Found at DESTRUCTIVE MARGINS - when oceanic crust is subducted and rises

12

Types of volcanic effects

Pyroclastic flows (nuee ardente)

Mudflows (Lahars)

Acid Rain

Volcanic gases

Lava flows

13

Volcanic Landforms at different plate boundaries

Ocean Ridges

Rift Valley

Young Fold Mountains

Deep Sea Trenches

Island Arcs

14

Where volcanic eruptions occur

Near
Constructive and Destructive plate margins

15

Volcanic eruptions at Constructive margins

Basaltic lava formed there
^^hot with low viscosity - easy flow and quick flow
^^ frequent eruptions and occur for a long time but aren't violent

OCEAN RIDGES formed when the margin is UNDERWATER and magma rises to fill any spaces left by moved apart plates

RIFT VALLEYS formed when the margin is ON LAND as the plates pull apart and come thinner so magma can break through

16

Volcanic Eruptions at Destructive margins

Acid lava formed here
^^cooler with more viscosity - less flow and slow flow
^^they erupt every once and a while and can be explosive in damage

these Violent Eruptions occur as at subduction zones, one plate is melted and magma is formed and rises to the surface - forms blockages in the vents - pressure build-up from the blockages

17

Island Arcs

crusts get subducted and melt when they reach a hot depth

a long chain of volcanoes are formed when hot remelted material from the subducting slabs rise and leak onto the crust forming a series of volcanos

they're formed on the opposite edge of a subducted slab - an ASSOCIATED SLAB AND TRENCH for each island arc

(Kuril Islands)

18

Ocean Trenches

Found at the bottom of the ocean - long narrow steep-sided depression (24-36 ft under the water)

Form in locations where one tectonic plate subducts under another. (Cont-Oceanic)

(Mariana Trench - Mariana Islands with 36.2 ft at deepest point)

19

Ocean Ridges

Are found at every basin

symmetrical in cross section

formed when the margin is UNDERWATER and magma rises to fill any spaces left by moved apart plates

the convection currents beneath are rising in the mantle beneath the oceanic crust
=all formed and connected to make one global mid-oceanic ridge system
>>>>> ridge push and slab pull responsible for the spreading

(The Mid-Atlantic Ridge)

20

Rift Valley

its the low-lying land between lots of mountain ranges/highlands

flat floors that are long and narrow
=can be deepened from erosion

found on ocean basins and on land continents

occur at divergence zones/boundaries where the plates separate - sea floor spreading happens here

irregular and sparse distribution

(East African Rift System)

21

Young Fold Mountains

GEOSYNCLINES - an area of sea separates 2 plates and sediment settles in DEPRESSIONS on the sea floor

sediments becoming compressed into sedimentary rock gradually

2 plates move towards each other again- sea floor sedimentary rock becomes folded
= range of fold mountains as this sedimentary rock appears above sea level

ANTICLINES - when the rocks are folded upwards

SYNCLINES - when they're folded downwards

22

measuring volcanic Magnitude

using the VEI scale (Volcanic Explosivity Index)

grades volcanoes on a scale of 0-8
based on AMOUNT OF MATERIAL EJECTED and HOW HIGH THE MATERIAL IS BLASTED

0-1 - daily
2 - weekly (3477 eruptions)
3 - yearly (868 eruptions)
4 - tens per decade
5 - one per decade
6 - several per decade (39 eruptions)
7 - several per millennium (4 eruptions)

23

Spacial distributions of deadly volcanoes

75% of all volcanic material is erupted at constructive margins
25% is violently explosive

only 1/24 of all deadly volcanoes actually occur at the margins - mainly at destructive

lava - high silica content = more deadly as an eruption due to the risk

24

Some of the major causes of death in a DEADLY volcanic eruption

- starvation
-mudflows (lahars)
-ash flows
-tsunami
-disease

25

All active volcanoes now being monitored

satellites

- to detect volcano shape changes
- look at previous eruptions
- measuring gas emissions

(Mt Ruiz = governments ignored the signs which caused death)

scientists can get it wrong and the locals feel to rebel against the evacuation

26

Volcanic frequency / regularity

some active volcanoes erupting only once every 100,000 years or some are every few months/days

(Stomboli volcano [the stratovolcano] has been erupting almost every single day being frequent and regular

27

Volcanoes being random or regular

can be very regular intervals eruptions

can be dormant for hundred of years then erupt several times in quick succession

28

How can they be predicted?

the REGULARITY can help scientists predict when it might erupt again
- monitor changes in the shape of volcano
-and tiny earthquakes

29

Pyroclastic Flows (Nuee Ardente)

mixture of very hot gas, ash, volcanic rock

flows down the sides of the volcano

travels at high speed (more than 80km/h) flowing a long way (10-15km)

fast travel = happen with relatively warning
can cause widespread death and destruction (buried under debris + burning)

30

Mudflows (Lahars)

when volcanic material mixes wjtb large amounts of water (from rainfall/ice melt)

travels at high speeds (over 80 km/h)
flowing for a long way

can bury/destroy natural habitats, infrastructure, settlements

31

Acid Rain

volcanic gases reacting with water vapour in the atmosphere - falls or rains down as acid rain

can damage ecosystems

can cause stone / metal to deteriorate (businesses gone, roofs, buildings)

32

Lava Flows

lava flowing from the volcanic vent down the side of the volcano

lava flow speed + distance dependent on the TEMPERATURE and VISCOSITY and SLOPE STEEPNESS

most flows are relatively slow - have time to evacuate areas that will be affected

destroys anything in its path -burning, burying or knocking it down

33

Volcanic Gases

Lava containing carbon dioxide and sulphur dioxide
=released into the atmosphere as the volcano erupts

some of these gases able to be harmful to humans/animals when breathed in

can be heavy when in the air

34

Ash and Tephra fallout

Material ejecting from a volcano during an eruption and falls back to the ground

consisting of a range of sizes - large peices of rock weighing lots of tonnesto microscopic ash particles

heavy rock particles dropped earlier than the lighter ones - lighter ones such as ash travelling further away from the volcano

ash harmful if breathed in

finer material able to form a layer of thick thickness - kill vegetation, cause building to collapse, stop transport on roads and rails

TEPHRA
-when magma is fragmented by explosions
-can stay in the atmosphere causing GLOBAL VARIATIONS IN WEATHER PATTERNS
- can damage buildings or kill/injure someone

35

Natures of volcanic explosions

Eruptions being named after the location
= Stromboli eruption 'strombolian'

display one characteristic or lots of characteristics

Icelandic
Hawaiian
Strombolian
Vulcanian
Vesuvian
Krakaotoan
Pelean
Plinean

36

Icelandic eruption

Fissure type eruptions

Extremely hot LAVA SPURTS, MOLTEN

(Barbug?)

37

Hawaiian eruption

Central vent eruptions

Fiery fountain spurts to 100ft +
Runny hot lava

(Kilauea)

38

Strombolian eruption

Large clots of molten lava bursting out
=forms luminous clots combined

Stream down the sides and in the sky

(Irazu Volcano - Costa Rica)

39

Vulcanian eruption

Dense ash-laden gas clouds
= rise high above the peak

Steaming ash forms a white-ish cloud near the upper part of the cone

(Mt Paracutin)

40

Vesuvian eruption

Eruptions of large ash-laden gas volumes

A cauliflower shaped cloud

(Mt Vesuvius)

41

Krakatoan eruption (not in the book or notes)

Very violent eruption

Hot flows of lava

42

Pelean eruption

Violent eruptions with pyroclastic flows (|nuee ardente)

700*C hot flows containing glowing clouds

(Mayon - The Philippines)

43

Plinean eruption

Large amounts of lava and pyroclastic material ejected

MOST POWERFUL ERUPTIONS

44

Predicting :
The USGS volcano hazards programme

monitors a volcano to detect signs of change that could lead into an eruption

need to fully understand a volcano's behaviour to be able to monitor it on a continuous basis :

-earthquakes
-ground movement
-volcanic gas
-rock chemistry
-water chemistry
-remote satellite analysis

45

Predicting :
Seismic exploration

seismic waves being generated by eruptions/explosions and earthquakes,

arrays of SEISMOGRAPHS can be placed around a volcano
^^^^^ small explosions can be set off to generate seismic waves

(2003 - Mt Fiji - conducted around here to detect S + P waves
= gave scientists a better understanding of the structure of the volcano)

46

Whats the S-wave shadow zone?
Prediction : Seismic exploration

a zone where no S-Waves arrive is a magma body EXISTS BENEATH the volcano

47

Prediction :
Radar Use

when volcanologists cannot make direct observations of a volcano, they usually turn to seismic information to tell them whats happening

SEISMOGRAPHS CANNOT DETERMINE IF A VOLCANO IS ERUPTING

measured in velocities
=can warn when debris that's hurled up high begins to fall back towards its source

can also be used for tracking volcanic ash clouds
=dangerous for aircraft
=can stall engines or damage engines permanently

48

Prediction :
Drones

can monitor activity by capturing footage + collecting data in areas that are difficult to reach

use the aerial images to create a 3D map of the volcano - capture environmental changes around there

putting sensors on the drones or using INFRARED cameras to monitor thermal activities
^^^^^^^^^more cost effective