Lecture 2 Volcanoes 2 Flashcards
What does hawaii consist of, and what is special about them
multiple volcanic islands very far away from any plate boundaries
these islands sit in the middle of the tectonic plate known as the pacific plate
definition of plume
spreading out in the shape of a feather
what do mantle plumes consist of and how does it work
mantle plumes consist of extremely hot magma originating at the core-mantle boundary
- core heats up magma
- magma gets pumped up into mantle
- due to its high temperature it melts its way up through the mantle and rises up to the lithosphere
- the head of the mantle plume spreads out (mushroom) just below the lithosphere and melts the surrounding upper mantle rock
once the mantle plume meets the upper mantle rock, there are two possibilities:
what are they
- magma can gradually cool beneath the surface (creates lots of volcanic rock = igneous rock)
- the hot spot (magma beneath the surface) causes a volcanic eruption = hot spot volcanoes
hot spot volcanoes are fed by the pool of hot magma just below the surface
hawaiian islands is possibility 2
what is volcanic rock
igneous rock
what is a hot spot
magma beneath the surface causes volcanic eruption
what are hawaiian islands considered
they are a trail of hot spot volcanoes
why do we observe this trail of island and not just one huge volcanic island
because the mantle plane originates below the lithosphere, its position remains fixed and is not affected by the moving tectonic planes above it
as lithosphere moves, magma escapes onto the surface at different sites which creates multiple islands
what are the names of the hawaiian islands in order from oldest to youngest
and what is the name of the future island
Kauai — Oahu — Maui — Hawaii (Kilauea)
future: Loihi
why do people still travel to hawaii if the volcanoes are erupting
the composition of the magma here means there is far less risk = eruptions less violent
- more predictable
- safer: less silica = less sticker = less gases
Volcanoes like Kilauea erupt less violently and release a very fluid MAGMA that can flow much more
easily away from the eruption site.
what is special about the lava of shield volcanoes
magma (lava) is more fluid
(different shape)
give three examples of stratovolcanoes
mount saint helens, mayon, fuji
give three types of shield volcanoes
Maui, Mount Terror, Mount Karthala
what do mantle plumes do (shield volcanoes)
mantle plumes feed hot magma to shield volcanoes above hot spots
the magma contains some silica and aluminum from mantle rock (but not as much as in subduction zones)
what happens at subduction zones
huge amounts of silica and aluminum enter magma as one tectonic plate sinks beneath another
what does silica consist of + what is its chemical formula
consist of silicon and oxygen
SiO2
the deeper you go — the less abundant these (and aluminum become)
magma coming from shield volcanoes is less or more viscous than magma coming from stratovolcanoes and what does this have an impact on
its less, which has a huge impact on the shape of these volcanoes
what is viscosity (real definition + everyday terms)
resistance of a fluid (liquid or gas) to a change in shape or movement of neighbouring portions relative to one another
in everyday terms: how gummy, thick, or sticky a fluid is; how much a fluid resists or opposes flow
examples of things that are more viscous than water
honey, maple syrup, corn syrup, motor oil
what’s special about the magma from shield volcanoes
it can:
- travel greater distances
- spread out in thin layers
- slope gradually
- doesn’t get stuck or resist flow like viscous magma from stratovolcanoes
what is magma from shield volcanoes made of
iron and magnesium
- doesn’t contain much silica
lava solidifies to become what (in shield volcanoes)
the lava solidifies to form dense (high density or mass + volume) basaltic rock
what is basaltic rock
makes up the majority of ocean floor (due to all the volcanic activity in oceans)
how do shield volcanoes look
from above, they look like an ancient greek shield
- wide dome (circular mound that sticks out of the ground)
- gradual slope (not steep like stratovolcanoes)
A CALDERA MAY FORM
what does the wide dome in shield volcanoes consist of
many lava layers
when does a caldera form
may form (not always) when
surrounding stone collapses into hole/space that once contained
molten stone (magma) released as lava during an eruption.
what does silica do to magma (stratovolcano)
makes it thicker, stickier, and more resistant to flow
stratovolcano magma
lower density, higher viscosity
what does lava solidify to (stratovolcano - with silica)
lava solidifies to form a variety of rocks
ex: andesite
what is andesite names after and what is it
ANDES Mountains
- 52% - 63% by weight silica
what do stratovolcanoes look like
- narrower dome (the circular mound that sticks out of the ground)
- steeper slope
- they are what most of us picture when we imagine a volcano
A CALDERA MAY FORM
what are Cinder Cones
- tiny (generally less than 400 m tall)
- steep
- volcanoes made up of pyroclastic rocks such as scoria
what are cinder cones also referred to as
scoria cones
(the baby of the family)
what is pyroclastic rock
PYRO = greek for “fire”
CLASTIC = broken
how do pyroclastic rocks come about
pyroclastic rocks (like scoria) are rocks generated by volcanic activity and that consist of fragments of other rocks and minerals
what are pyroclastic materials
fragments less than 2mm in size
- we refer to as ash
what are scoria
bits of lava that harden in midair after being ejected by a volcano’s gases
how do cinder cones erupt
- can be very violent
- eject molten pyroclastic materials (scoria) into the air
what is the shape of cinder cone and why
- steep in shape
because scoria does not fly far from the volcano’s vent (hole)
what are lava domes
- volcanic domes
- less violent (because magma is thick so it can’t do much type shi)
- very small volcanoes that possess extremely viscious (thick) magma and lava
whats special about lava in lava domes
lava does not move far at all and continues to pile up just outside the volcano’s vent (hole)
where are lava domes found
next to larger stratovolcanoes
give two examples of places that contain cinder cones
California, USA
and
B.C., Canada
give two examples of lava domes
mount saint helens has one (Washington State, USA)
and
the Santa Maria volcano in Guatemala also has one
