Transcript File - Mr. Haan`s Science

Chapter 10 page 279
A. NATURE OF VOLCANIC ERUPTIONS
1. Factors affecting Eruptions
a. Viscosity
1) Resistance to flow
2) More heat = less viscous
3) As lava cools it becomes more viscous until
movement stops
4) More silica = more viscous
5) Explosive eruptions typically have more viscous
lava
b. Dissolved gases
1) Provide force to eject lava from vent
a) Vent – opening to surface in volcano
b) Magma moves towards surface
c) Pressure is reduced allowing quick release
of gases
2) Mostly water vapor and CO2
3) Low viscosity lava
a) Gases escape easily
b) Quiet eruption – Hawaii
4) High viscosity lava
a) Gases collect in pockets and increase in size
b) Explosively released
c) Mt. St. Helens
2. Volcanic Material
a. Lava flows
1) Pahoehoe
a) 19 mph
b) “Ropey” look
c) Could have liquid subsurface
2) aa
a) Slow moving
b) Very sharp edges
LAVA COMPARISON
Pohoehoe
Aa
3) Pillow lava – forms
underwater
Formation
http://www.youtube.com/watch?v=gn_IW5Vsxaw
b. Gases
1) Escape as soon as pressure decreases
2) 1 – 6% of total weight
3) Amounts
a) 70% water vapor
b) 15% carbon dioxide
c) 5% N and S
d) Last 5% combination of Cl, H, Ar
4) First sign of eruption
c. Pyroclastic materials
1) Ash
a) Very fine glassy fragments
b) Can suffocate people
c) Can travel around earth
d) Bad for engines
e) Can cool global temps
f) Slippery when mixed w/water
g) Hardens into “concrete”
2) Blocks (cinders) – larger than ash
3) Bombs
a) Lava which solidifies in air
b) Up to several tons
c) Usually within 2 miles of vent
d. Fumaroles
1) Vents in ground
2) Gas and steam escape
a) Heavier than O2
b) O2 becomes displaced
c) Very dangerous
3. Types of Volcanoes
a. Anatomy
1) Volcano – lava and pyroclastic materials
building a mountain
2) Vent – opening to the surface
3) Crater – steep-walled depression at summit
4) Conduit – pipe leading to vent
5) Magma chamber – holds magma
b. Shield
1) Often come from ocean and form islands
https://www.youtube.com/watch?v=CsKTzBZNjtE
2) Dome shaped w/flat slopes
3) Runny lava and quiet eruptions
https://www.youtube.com/watch?v=byJp5o49IF4
c. Cinder cones
1) Ejects mostly cinders, but also ash and bombs
2) Steep slopes (angle of repose)
3) Gravel interlocks preventing it from sliding
4) Single short eruption
a) Can last days – a few years
b) Pipe solidifies and never erupts again
• https://www.youtube.com/watch?v=aS_xl3nu_mY
d. Composite cones
1) AKA stratovolcanoes
2) Most dangerous
3) Alternate lava and pyroclastics
4) Larger than cinder cone
5) Symmetrical
6) Ring of fire
https://www.youtube.com/watch?v=1u1Ys4m5zY4
MOUNT FUJI
7) Dangers
a) Pyroclastic flows (124 mph)
http://www.youtube.com/watch?v=yvG_N7eqMWk
b) Lahars
i. Mudflows
ii. Caused from melting ice and snow,
heavy rains, caldara wall failing
iii. Can happen without an eruption
MOUNT VESUVIUS
MOUNT SAINT HELENS TREE
DAMAGE
• http://www.youtube.com/watch?v=kznwnpNTB6k
4. Volcano activity
a. Active – erupted w/in historical times or could
erupt at any time
b. Dormant – hasn’t erupted recently but still
could
c. Extinct – no record of eruption and no activity
by volcano
d. Could change classification
https://www.youtube.com/watch?v=zJgwNqzumL8
5. Other volcanic landforms
a. Caldera
1) Large depression
2) Magma chamber collapses
3) Large eruption
Deepest lake in USA at
1949 ft
One of the clearest lakes in
the world due to no inflow
or out flow
Wizard Island in the middle
b. Necks
1) Volcano erodes away
2) Neck is left
c. Pipes
1) Feeds magma to volcano
2) Could form diamonds
NECKS
Devil’s Tower – Wyoming
Ship Rock – New Mexico
d. Lava Plateaus
1) Covers large areas
of land
2) Low viscosity lava
comes from fissures
B. INTRUSIVE IGNEOUS ACTIVITY
1. Plutons (intrusive igneous bodies)
a. Structures formed from cooling/hardening of
magma below crust
b. Classified by size, shape, and surrounding rock
c. Sills and laccoliths
1) Magma intruded close to surface
2) Form parallel to sedimentary rock layers
d. Dikes – magma
cutting across rock
layers in fractures
e. Batholiths – surface
exposure greater than
100 square kilometers
2. Origin of Magma
a. Role of heat
1) Geothermal gradient
– Δ in temp. w/depth
2) Friction – near
subduction zones
3) Mantle rocks can rise
heating rocks
b. Role of pressure –
Increase pressure =
increase melting point
c. Role of water – Causes
rocks to melt at lower
temperatures
C. PLATE TECTONICS AND IGNEOUS ACTIVITY
1. Convergent plate boundaries
a. Oceanic crust pushed into mantle
b. Pressure and heat increase and water lowers
melting pt.
c. Rocks melt and rise through cracks
d. Types
1) Ocean-ocean – can form islands
2) Ocean-continent
2. Divergent Plate Boundaries
a. Plates moving apart
b. Magma rises to fill rift
c. Sea floor spreading
3. Intraplate Activity
a. Happens in middle
of plate
b. Mantle plume rises
toward surface
c. Causes hot spots
d. Hawaii and
Yellowstone
D. HEATED GROUNDWATER
1. Hot springs
a. Heated water rises
b. Heated by magma intrusion or depth
2. Mud pot
a. Hot spring surfacing in volcanic ash
b. Muddy bubbling spring
http://www.youtube.com/watch?v=R1liFUqHhvY
HOT SPOT AND
MODIFIED
GEOTHERMAL
GRADIENT
3. Geysers
a. Thermal spring that shoots water from ground
b. Magma heats water in twisting chamber
c. Superheated water rises in temp until pressure
can’t keep it as a liquid
d. Immediately turns to steam
Yellowstone Geysers
http://www.youtube.com/watch?NR=1&v=so5pix18jM0&feature=endscreen
E. VOLCANO SAFETY
1. Stay away from active volcanoes
2. Survival kit
a. Flashlight
b. Battery-operated radio
c. Batteries
d. Goggles and mask
3. Know evacuation route
4. During
a. Evacuated only as recommended to avoid
lava, mud flows, flying rocks and debris
b. Avoid river and low-lying regions
c. Wear long sleeves and pants
d. wear goggles or eyeglasses – take out
contacts
e. Wear mask or damp cloth over face
5. Not leaving
a. Close windows,
doors, block chimney
and vents
b. Ash puts extra stress
on roof – clean it off
c. Damages engines
and metal parts – drive
below 35 mph