Transcript Lassen Peak Volcanic National Park

On Sunday, May 18, 1980, the largest volcanic eruption to occur in
North American historic times transformed a picturesque volcano into
a decapitated remnant. On this date in southwestern Washington
State, Mount St. Helens erupted with tremendous force.
Before
After
What happened??
Mt. St. Helens
•Approximately 1 km3 of ash erupted.
•Summit decreased by 1,350 feet.
•Claimed 59 lives
•Ash propelled 11 miles into the atmosphere.
•Ash covered surrounding areas of Yakima, Tri-cities, and
northern Oregon for 3 days – Noon felt like night.
• Feb. 1981- highest birth rate in Portland and surrounding
areas –TRUE FACT
Advice from the authorities:
If there is another major eruption, put your head between your
legs and kiss your ash goodbye!
The “buzzword” is VISCOSITY
What is viscosity?
Viscosity = how well a material flows
more viscous – flows very slowly
(high viscosity)
less viscous – flows quickly
(low viscosity)
Does glass have viscosity?
5
Why do volcanoes have different eruptive
•high viscosity styles???
•high SiO2
Factors influencing eruptions
•felsic
• dependant on the magma’s viscosity
•“pasty”
•explosive
• high viscosity –”pasty” explosive
• low viscosity –”fluid” flows easily
A
•low viscosity
•low SiO2
•mafic
•“fluid”
•non-explosive
B
Factors influencing viscosity
• Temperature of magma
• T
• T
viscosity
viscosity
= fluid flow
= pasty flow
• Chemical composition
• SiO2 content (high or low)
mafic composition: (50% SiO2)=“fluid” flow
intermediate comp.: (60% SiO2)
felsic composition: (70% SiO2) =“pasty” flow
Dissolved gasses – influencing the movement of magma
(volatiles – water, CO2, SO2….)
Silica content and volatiles erupt two types of materials:
Gas charged lava
expands 100 times its volume
lava fountains
Gas charged
expands 100 times its
volume
very explosive
lava flows fluidly
volatiles easily migrate upward
magma low in SiO2
Volatiles migrate upwards
with difficulty
magma high in SiO2
sulfur dioxide
> 1%
SO2
5%
Carbon dioxide
water vapor
70%
15%
5%
volatiles
Dissolved gasses (volatiles)
• 1-6% of total magma wt.
Magma chamber
• contributes to atmosphere
Types of Basaltic Lava Flows
(low silica (SiO2) content)
Pahoehoe
Aa
• very fluid, thin,
broad sheets
• very “pasty,” sticky,
thick, cool flows
• flows 10-300 km/hr
(30-900 ft/hr)
• flows 5-50 m/hr
(15-150 ft/hr)
•high volatile gas content •low volatile gas content
• smooth “skin,” ropey
type flow
• rough, blocky, sharp,
angular type flow
Pyroclastic materials
Ash
Volcanic
Bombs
Bombs
Nuee-Ardente Lahars
Lahars mud flows
Ash
Ryholitic magmas
• high silica
• very explosive
Nuee-Ardente
• thick, pasty
• high viscosity
• pyroclastic ejections
Four (4) types of Volcanoes
•Volcano type is dependant on
SiO2 content.
shield
composite
(stratovolcano)
cinder cone
Explain the differences.
plugged dome
Shield Volcano - Hawaii
Broad, low angle flanks
Shield Volcanoes
•Hawaiian Islands, Iceland, Galapagos Islands
•commonly rise from the deep ocean floor
•formed by the accumulation of fluid basaltic flows
•low silica content (basaltic composition)
•low viscosity
•less than 1% pyroclastic debris
•non-explosive eruptions
•pahoehoe flows
•aa flows
Stratovolcano
Composite Cones (stratovolcanoes, stratacomposite)
•Western U.S. coast, Western South American coast, Japan
• typically form in the ocean along continent convergent boundaries
• found along the ring of fire
Steep high angle flanks
•Formed from layering deposits of
ash, lava, and pyroclastic flows
•High silica content (70%)- (Rhyolitic
composition)
•high viscosity flows
•Abundant pyroclastic activity
•deadly airborne debris
•Explosive eruptions – very hazardous
Cinder Cones
• Exist all over the Earth’s surface
• Typically, located in volcanic fields (Flagstaff AZ-600+)
•Formed by gas rich basaltic flows (low viscosity, low silica)
producing small sized material. Common
rock scoria and volcanic glass
•Single eruptive episode lasting
a short time
•Composed of scoria and loose
pyroclastic material
• Commonly forms along the
flanks of preexisting volcanoes
•Very high, steep angle flanks
30-40 degrees
• average 100 – 1000 feet
Cinder Cones
Lava Dome (plugged dome volcano)
• results from viscous lava extruding into the crater.
• high degassing of extrusion  “pasty – sticky” lava
• most preserved domes are chemically high SiO2 content
• commonly rhyolitic or dacitic in composition
Rhyolitic / Dacitic
lava plug
High SiO2
Plugged Dome Volcano
Plugged Dome
• Proclaimed has a National
Monument in May, 1907
• Eruption of Lassen Peak
May, 1914
• Subsequent eruptions between
1914 – 1921
• Lassen Volcanic National Park
established August 9, 1916
The Ring of Fire
Cascade Mt. Range
Stratovolcanoes
17
Baker
Pacific Plate
Rainier
St. Helens
Adams
Hood
Jefferson
North
American
Plate
Three Sisters
Newberry Volcano
Crater Lake
McLaughlin
Medicine Lake Volcano
Shasta
Lassen Peak
Ocean to Continent
Convergence
Oceanic plate is subducted
beneath continental plate.
Melting plate ascends
upward mixing with
continental material.
• High SiO2 – High viscosity
• explosive volcanoes
• “pasty” lava flows
• composite type volcanoes
• andesite/rhyolite rocks
Common Volcanic Rock Types
Lassen Peak National Park
Black Dacite
Banded Pumice
Light Dacite
Andesite
Dacite eruption from 1915
• 63% to 68% SiO2
• plagioclase feldspar, amphibole, pyroxene
• erupted around 800-1000 0C
$0.25
plagioclase feldspar
(Mount Tehama)
volcanic base of
Mount Tehama
Mount Tehama caldera (Brokeoff Volcano)
• exploded and collapsed during Late
Pleistocene leaving volcanic remnants
• “Huge” composite volcano
• 3 ½ mile wide volcanic caldera
• Lassen Peak formed on the northern
flank of Mount Tehama
Projected cross-section of
Mount Tehama
Mount
Diller
Mount
Brokeoff
Estimated
11,000 feet +
Sulfur Works
Bumpass Hell Hot Springs
• Hot springs, fumaroles, strong rotten egg odor indicates the
presence of hydrogen sulphide (H2S)
• Represents the center of Brokeoff cone (Mount Tehama)
• Results of hydrothermal alteration:
• hard gray-green andesite lava  bright colored clays
• other volcanic rocks  reduced to red iron oxides
• presence of sulphuric acid (H2SO4)  rapidly
reducing volcanic rock to clays
• High water acidity  pure opal (not gem quality)
Bumpass Hell – Named for a cowboy that
worked in the area in the 1860’s
(Kendal Bumpass)
Scalded his feet and when ask where he was, he
replied ------ IN HELL
Devil’s Kitchen
• Strongly acidic resulting in holes
and pits eaten in bedrock
• Sulfur Works, Bumpass Hell, Devil’s
Kitchen associated with a north-west
trending fault system
• Less civilized than Bumpass Hell and
6000 feet elevation
• Relatively small hike from Bumpass
Hell with a 440 feet elevation gain
• Stepping back into the Mesozoic!
Lassen Peak Statistics:
• Stands 10,457 feet to summit
• Located at northern end of the Sacramento valley
• Landmark for immigrants entering the valley
(around the 1800’s)
• Named after Peter Lassen, Danish blacksmith
(1830)
• Peter Lassen guided parties of immigrants into
California using Lassen Peak, but frequently
got lost ---- as the story goes.
Lassen Peak Geologic History
• Radiometric dating shows the
formation of Lassen Peak around
31,000 years ago --- along the
northern flank of Mount Tehama
• Streams of dacitic lava flows moved
to the north reaching 1500 ft covering
20 mi2
• 25,000 -31,000 years, Lassen grows
rapidly reaching 1800 ft in a few
years --- becoming the largest
plugged dome type volcano
• 18,000 – 25,000 years, Lassen Peak
significantly altered by glaciation
• 30 additional smaller steep-sided
dacitic domes form (Bumpass Mt,
Helen Ridge, Eagle Peak, Valcan’s
Castle, Reading Peak
Lassen Peak Geologic History
• 300 – 1100 years, several dacitic
pumice domes form with abundant
avalanches producing topography
similar to the Chaos Crags deposit.
This resulted in the Chaos Jumbles
deposit and the damming of
Manzanita Lake
• Mid 18th century, formation of Cinder
Cone (NE-section of the park). Ash
falling on the streams of lava resulted
the formation of Painted Dunes.
avalanche debris
A flow of quartz-studded basaltic lava
flows from Cinder Cone damming Butte
and Snag Lakes
May 22, 1915
1914 -1921 Lassen Peak Activity
“The Great Explosion”
Eruptions seen as far as 150 miles away
Subsequent eruption
1915
Explosions recurred at irregular intervals
on Lassen Peak for most of 1914. Later, on
May 19, 1915, a mass of lava rose in the
summit crater and spilled 1,000 feet
(300 m) down the western side of the
volcano. Extensive lahars (mudflows) were
created on the northeastern side as snow
banks were melted.
A great explosion blasted out a new crater
three days later on May 22, 1915. A volcanic
cloud rose 40,000 feet (12,000 m) along with
flowing lava creating various dams and
lakes currently observed today. Volcanic
activity declined, finally ending in 1921.
Lassen Peak
Cinder cones producing
Eagle Peak and Bumpass
Mountain. Photo taken in
the southwest direction.
Eagle Peak
Smaller cinder cones
compared to the plugged
dome Lassen Peak
Bumpass Mtn
Lassen Peak
Chaos Crags
(older)
Avalanche debris produced on
the north side of Lassen Peak
between 300-1100 years
Sept 2006
Chaos Jumbles
(younger)
Oct, 1930
Painted Dunes
The Painted Dunes are
composed of oxidized cinders
lying over the Fantastic Lava
Beds. In the distance, the
concave flank (right side) of
Lassen Peak is where the
lahars blew down the peak in
1915 to create the Devastated
Area.
shield volcano
Avalanche
deposits
Painted Dunes
Plugged Dome
Composite cone
(Mt Tehama)