volcanic eruptions Flashcards
(27 cards)
what are the two types of volcanic eruption?
- EFFUSIVE eruptions
- EXPLOSIVE eruptions
what are characteristics of EFFUSIVE eruptions?
more gentle, free-flowing basic eruption of basaltic lava
* DIVERGENT plate boundaries
* BASALTIC lava
* basic (low % silica), LOW VISCOSITY, HIGH TEMP at eruption
* not violent as GAS BUBBLES EXPAND FREELY
* gas+ lava flows produced
* MOREB FREQUENT+ eruptions can last for months
* forms SHIELD VOLCANOES with GENTLY SLOPING SIDES (formed by LAVA PLATEAU- eruption from multiple fissures)
* basic lava flows freely + covers large areas (FLOOD BASALTS)
example of effusive eruptions
ICELAND- many large shield volcanoes as above mid Atlantic ridge (divergent boundary so effusive eruptions occur)
what are characteristics of EXPLOSIVE eruptions?
VIOLENT eruptions due to build up of pressure- viscous lava (andesitic/ rhyolitic- high silica content) which prevents escape of dissolved gases
* CONVERGENT plate boundaries
* RYHOLITIC/ ANDESITIC lava
* ACIDIC (high % silica)
* violent BURSTING OF GAS BUBBLES when magma reaches surface
* LAVA BOMBS, TEPHRA, ASH
* LOWER FREQUENCY+ can be INACTIVE for long periods of time
* steep- sides COMPOSITE STRATO- CONE VOLCANOES - CALDERAS form when collapses
* made up of layers of ash+ acidic lava (SILLS and DYKES)
* acidic lava does not flow easily
example of a composite strato- cone volcano
ST. HELENS, USA- has a caldera too
what is a HOTSPOT?
- when an eruption occurs not at a plate boundary
- a PLUME OF MAGMA rises from the mantle+ erupts at the surface
- a FIXED ARES of INTENSE VOLCANIC ACTIVITY- eruptions of BASALTIC LAVA
e.g. HAWAII (chain of volcanoes)- middle of PACIFIC PLATE- the plate moves over the plume (pacific plate moves 10cm/year), forming new SHIELD VOLCANOES - pyroclastic flows occur in Hawaii
what features are found at EXPLOSIVE eruptions?
- composite strato- cone volcanoes, with dykes+ sills, and a plug of solidified magma
- calderas- empty magma chamber so collapses in on itself
what features are found at EFFUSIVE eruptions?
- lava plateaus/ flood basalts
- shield volcanoes (free- flowing lava runs off and cools)
what is a LAVA PLATEAU/ FLOOD BASALT?
magma erupts from multiple fissures (FREE-FLOWING LAVA)
at effusive eruptions
what are SHIELD VOLCANOES?
EFFUSIVE eruptions at DIVERGENT plate boundaries (MID-OCEAN RIDGES)
most unseen on ocean floor, except ICELAND above MID-ATLANTIC RIDGE
if successive flows accumulate for long time, huge volcanoes extending horizontally for 10s of km can form (e.g. Skjaldbreidur- Iceland)
what is the name of the scale used to measure volcanic eruptions?
VEI- Volcanic Explosivity Index
how does the VEI SCALE work
- measures MAGNITUDE (amount of material erupted) and INTENSITY (speed erupted)
- scale of 0-8 (least to most explosive)- LOGARITHMIC SCALE
what type of eruption is 0-2 on VEI scale?
what type of eruption is 4-5 on VEI scale?
what type of eruption is 7-8 on VEI scale?
- effusive
- explosive
- super volcanoes
what classifies a volcano as a SUPERVOLCANO?
1000km3 of material erupted in one eruption
magnitude 7-8 on VEI scale
what is the life cycle of a SUPER VOLCANO?
- BEFORE ERUPTION: magma rises and builds up in magma chamber+ pressure builds
- SUPER ERUPTION: pressure becomes too much and a catastrophic eruption occurs (huge amounts of ash, gas, and magma)+ land above collapses forming a caldera
- AFTER ERUPTION: volcano becomes dormant (for thousands of years)
- RESURGENCE: magma chamber may start to refill; small eruptions/ bulges can occur
pressure slowly builds again (back to stage 1)
what is an example of a SUPER VOLCANO?
YELLOWSTONE- Wyoming, USA
has a 75km caldera
what HAZARDS are produced by VOLCANIC ERUPTIONS?
- pyroclastic flow
- tephra
- toxic gases
- lahars
- floods
- tsunamis
how can the impact of these eruptions be deduced?
depth+ extent of ash layers
impact on plants, insects, animal species (paleobiology)
on what scale are SUPERVOLCANOES HAZRDARDOUS?
GLOBAL SCALE- e.g. trigger global dimming/ air space disruption
Yellowstone supervolcano eruption- impacts
2 mil years ago- temporary climate change (TEMPS DECREASED 2°) due to eruption of ASH+ GAS+ PARTICULATES carried in upper atmosphere (GLOBAL DIMMING+ COOLING)
500 miles affected by ash
HOTSPOT under yellowstone- HEATS+ STRETCHES+ WEAKENS CRUSTAL ROCKS - volcanic activity could occur anytime (HARD TO PREDICT)
What is a PYROCLASTIC FLOW?
Hot flows of gases and tephra (500°C+)
High speeds (100km/h)
Destroy everything in path
Hot poisonous gas causes instant death (e.g. Pompeii)
What is TEPHRA?
Material erupted
Size varies from FINE ASH to VOLCANIC BOMBS
can DESTROY CROPS+ BURY FARMLAND in ash layers
DISRUPTED TRANSPORT, COLLAPSES BUILDINGS, causes RESPIRATORY diseases
What are TOXIC GASES?
E.g. CO, CO2, SO2 -deadly
SO2 (sulphur dioxide) combines with water vapour in atmosphere to create ACID RAIN- enhances WEATHERING (can damage crops+ cause environmental pollution)
What are LAHARS?
example?
ASHY MUDFLOW
SNOW+ ICE on volcano summit MELTS during eruption
Flows rapidly down cone (50km/h)
Mixes with tephra erupted
Destroys everything/ covers it in debris+ ash
SOUTHEAST ASIA- ASH COVERED SLOPES of volcanoes continue to generate labars after periods of HEAVY RAIN
