GLY 3163: OLYMPIC + CASCADE VOLCANOES
Crater Lake
(21 square miles in size and 1900 ft deep) Crater Lake was formed after the collapse of an ancient volcano, posthumously named Mount Mazama. This volcano violently erupted approximately 7700 years ago. That eruption was 42 times as powerful as the 1980 eruption of Mount St. Helens. The basin or caldera was formed after the top 5000 feet of the volcano collpased
The Phantom Ship in Mt. Mazama
-Remnant of a volcano that existed before Mount Mazama. It was covered by the younger volcano and later exposed when the caldera formed
Dehydration - hydration partial melting typically occurs in subduction zones
-The down-going plate contains water bound in minerals -This water is released when the minerals are heated as the plate descends into the hot mantle -The water is released as a super critical fluid, which rises and causes the overlying mantle to partially melt via hydration melting -These partial melts are H20-rich because they are formed by hydration melting -The partial melts rise, pool, and may eventually freed volcanoes at subduction zones like Mt. Pinatubo (Phillippines), Mt. St. Helens (USA), or Mt. Fuji (Japan) -These magmas have high concentrations of H20 and moderate to high SiO2, which often lead to explosive volcanic eruptions; following magma composition is most explosive: high silica, high water
Sun Notch and Kerr Notch in Mt. Mazama
-U-shaped glacial troughs beheaded by the explosion of Mount Mazama
Mount Rainier National Park, Washington
-Volcanic mudflows (lahars) are the main natural hazard in the Mount Rainier region -Hot water alters the volcanic rock to soft clays (hydrothermal circulation) [this also forms mineral deposits] -Glaciers provide additional water -Rock/water mixture speeds down the steep slopes
Cascade Volcanoes
A Continental Volcanic Arc The Cascade Volcanoes lie above the line at which the top of the Juan de Fuca plate is deep enough - 75 to 100km (~50 miles), so that it is hot enough to dehydrate
ACCRETIONARY PRISM (WEDGE)
A cross section along line A-Aʼ reveals how the rocks of Olympic National Park were manufactured in the sea, carried eastward by the Juan de Fuca Plate, then scraped off and incorporated into the
The Hoh River
A gravel bar along the Hoh River in the vicinity of the Hoh rain forest shows how eroded sediment is transported out of the high mountains. The sediment is eventually deposited in the shallow and deep ocean. The deep water sediments are eventually scraped off in the subduction and accreted to North America again. The wedge is a giant recycling machine.
Gray colors in Mt Rainier are due to
ANDESITE lava flows Volcanic mudflows (LAHARS) Relatively high-silica lava produces a steep-sided composite volcano with a history of some explosive and some non-explosive eruptions
How did eruption occur in Mount Mazama? How did erosion happen in Mt. Mazama?
Ash rises high into the air blanketing a wide area with varying thicknesses of ash and dust Pumice and gas-laden materials flow down the sides of the mountain Top of mountain collapses as rubble falls into the nearly-empty magma chamber Low-silica eruptions coat the bottom of the large crater (caldera) Rainfall and snowmelt partially fill the caldera, forming Crater Lake These Pinnacles, about 5 miles southeast of the caldera rim, were fused by hot gases escaping through many feet of ash after the eruption Erosion removed the thick layers of loose ash leaving the resistant pillars standing deep in Sand Creek The light area in the deeper part of the canyon in welded tuff with rhyodacite composition -- the Wineglass welded tuff, which erupted first from the top of the magma chamber The darker upper layer has an andesitic or basaltic composition and erupted last
Rainier is being eroded by several large Glaciers. These rapidly cut into the Volcanic rocks of the summit and transport Rock materials to lower elevations
At about 3,520 feet in elevation, the terminus of Carbon Glacier on Mount Rainier is the lowest in the lower 48 states. The photographs show moraine and outwash deposits The Carbon River drains from the terminus of Carbon Glacier. The terminus of the glacier is a very unstable environment where ice and rock debris calve frequently from the advancing glacier
Glaciated peaks of the Olympic Range (USGS).
Cenozoic sedimentary rocks mixed with submarine lavas were scraped off the subducting ocean floor by plate convergence and pushed up into a jumbled heap on the Olympic Peninsula.
Olympic National Park, Northwest Washington
Coastal Ranges contain materials that were deposited and erupted in the ocean, then scrapped off the subducting Juan de Fuca Plate and incorporated into an ACCRETIONARY WEDGE.
Crater Lake National Park
Collapsed Caldera in Crater Lake Mazama pyroclastic flow deposits Wineglass welded tuff
CRATER LAKE NATIONAL PARK
Crater Lake lies in the caldera of a collapsed volcano (Mt. Mazama) Features within Crater Lake National Park include: Collapsed caldera, deepest lake in the USA (1,943' deep), cinder cones, satellite craters, plug domes, a pumice "desert" and pinnacles of pumice
What are dikes? What are lava domes made out of?
Dikes are the cooled remnants of the volcano "plumbing" system Lava domes like Lano rocks are made of sticky lava (rhyolite-to-dacite)
Cascade eruptions in Crater Lake over the past 4,000 years
From top to bottom: Mount Baker Glacier Peak Mount Rainier Mount St. Helens Mount Adams Mount Hood Mount Jefferson Three Sisters Newberry Volcano Crater Lake Medicine Lake Volcano Mount Shasta Lassen Peak
Mt. St. Helens National Volcanic Monument, Washington
High-silica lava generated in subduction zones can be thick and viscuous leading to: -Steep composite volcanoes -Explosive eruptions -Lava domes
MOUNT RAINIER NATIONAL PARK
Is a 14,411' stratovolcano Gibralter Rock, Steamboat Prow, and Willis Wall are erosional remnants of the volcano's cone when the summit was at its maximum elevation, 75,000 years ago
Accretionary Prism
Jumbled and broken sediment layers are visible in this sea stack at Rialto Beach
This view is looking east toward Mount Storm King at the east end of the lake.
Lake Crescent is in the northwest corner of Olympic National Park. This natural glacial lake is all that remains of a great valley glacier that filled the valley during the late Pleistocene ice age.
Topography
Large composite or strato volcano with many large glaciers feeding rivers in U-shaped valley Geological map: 0-2 million year old andesite on top of older Eocene to Miocene volcanic rocks and the Miocene aged Tatoosh Pluton (intrusion of granodiorite)
Formation of Pillow Basalt
Lava erupts into cold ocean water and freezes, resulting in dark heavy basalt pillows 1) hot LAVA rises through the Oceanic Crust 2) molten Lava finds paths through older pillow basalts until it erupts into the cold ocean 3) LAVA rapidly cools from all directions as it erupts into the cold ocean water forming pillows
How does the Mazama eruption and caldera collapse reveal the internal structure of a stratovolcano?
Layers of ash, lava and lahars appear horizontal on the cliffs, but dip away on the flanks of the volcano. Strato or composite volcano includes andesite, basalt, dacite, rhyolite; the mazama eruption did not start off as andesite and end as rhyodacite
Hillman Peak in Mt. Mazama
Measures 8,100 feet long A parasite cone of Mount Mazama now cut by the blast and eroded by ancient glaciers. The peak probably stuck up like a ridge between two large glaciers Grooves from glacial scouring on Mt. Mazama long before the eruption
Chemical composition of the igneous rocks
Most of the volcanic (extrusive) rocks on Mount Rainier are Andesite Some are also Dacite, which is between andesite and rhyolite in silica content The magma forms due to subduction in the mantle above the down-going oceanic plate and is mixed with magma from the lower crust | Basalt Andesite Rhyolite SiO2 48.36 60.10 72.08% TiO2 1.32 0.71 0.37% Al2O3 16.84 17.20 13.86% Fe2O3 2.55 2.22 0.86% FeO 7.92 3.53 1.67% MnO 0.18 0.10 0.06% MgO 8.06 3.50 0.52% CaO 11.07 7.10 1.33% Na2O 2.26 3.30 3.08% K2O 0.56 1.30 5.46%
Eruption of Mount Mazama (eruption history revealed in paintings by Paul Rockwood)
Mount Mazama was a 12,000 foot composite volcano (with one or more summits) Magma collected in a region ("magma chamber") a few miles below the surface High-silica magma rose to the top, leaving heavier, low-silica magna on the bottom The large event began 7,700 years ago with high-silica eruptions
Mt. Rainier
Mount Rainier is the highest and third most voluminous volcano in the Cascade Range. It is potentially the most dangerous volcano in the range because of the large population living around its lowland drainages. These areas are at risk because of the mountain's great relief and the huge area and volume of ice and snow on the cone
Mount St. Helens
Mount St. Helens was known as the "Fuji of America" because its symmetrical beauty was similar to that of the famous Japanese volcano. The graceful cone top, whose glistening cap of perennial snow and ice dazzled the viewer, is not largely gone. On May 18, 1980, the missing mountaintop was transformed in a few hours into the extensive volcanic ash that blanketed much of the Northwestern United States and into various other deposits closer to the mountain. Is now (not?) considered a dormant volcano
Cascade Range: Volcanic Mountain Range (higher to lower)
Mt.Baker Glacier Peak Mt. Ranier NP Mt.Adams Mt. St. Helens NVM Mt. Hood Mt. Jefferson Three Sisters Mt. Shasta Lassen Volcanic NP
The CORE AREA is made of sedimentary layers uplifted from the ocean floor above the subduction zone.
Much of the rock was metamorphosed, deformed and tilted during accretion.
CASCADE VOLCANOES
National Parks in the Cascade Volcanoes 1. Mt. Rainier 2. Mt. St. Helens 3. Crater Lake
CRESCENT TERRANE
Oceanic basalt Volcanic lava flow rocks in Olympic National Park are dark and heavy basalt.
What forms the Coast Ranges?
Oceanic sediment and basalt scraped off the subducting Juan de Fuca plateWhat
Crescent Terrane
Older basalt of the Crescent Terrane Is thrust over top of the younger Core Area rocks. Uplift and Erosion has exposed the younger Core Area rocks within the arc of the Crescent Terrane.
Mount St. Helens eruption
On May 18, 1980, the explosive eruption of Mt. St. Helens was etched in history as one of America's major natural disasters
Wizard Island, cinder cones, and Merriam cone in Crater
Opportunity to see the internal architecture of a volcano using imaging of the lake bottom
Mt. St. Helens eruption, Washington
Prior to 1980: Steep composite volcano Small eruptions in spring 1980 Early 1980: Bulge on North side of mountain (by may 17, bulge had grown over 450 feet) Prior to May 18, 1980: Magma rising, bulge formed, small eruptions May 18, 1980: Earthquake-->landslide, lateral blast, eruption cloud, ash fallout Explosive eruption, eruption cloud (cloud of volcanic ASH [see next slide]), lateral blast at the start of the eruption, collapsed North side of the volcano with mud flow in Spirit Lake, trees blown over by the lateral blast, mud and ash deposits, glacial melt cavities From 1980 to 1986, a Lava Dome formed. Other dacite lava domes have formed more recently. 1,200 feet elevation loss After boiling down a once-wooded slope, this mudflow steams and gurgles, covered with ash and strewn with logs along what remains of Spirit Lake's south shore. The mudflow was a mixture of volcanic ash, material from the volcano itself and water from melted glaciers and Spirit Lake
Sea Stacks and the Olympic Coastline
Sea stacks at Ruby Beach show land uplifted out of the ocean and then partly eroded. The balance between uplift and erosion determines the height of the land surface and mountains of Olympic National Park. Studies suggest a balance over millions of years. Cross section shows uplift, sea level changes, deposition, and erosion during Quaternary time. Tectonic uplift and glacial episodes caused sea level to fluctuate over time.
Deposits in Olympic
Stream deposits cover older sedimentary layers in the western part of the park. Glacial deposits cover older sedimentary layers in the northern part of the park.
What forms Cascade Volcanoes?
Subducting plate dehydrates (Coast ranges: Puget Sound and the Willamette Valley are low-lying regions between the rising mountains.)
What forms the Coast Ranges and Cascade Range in Olympic?
Subduction of the Juan de Fuca Plate forms both the Coast Ranges and the Cascade Range
What is the Crescent Terrane?
The CRESCENT TERRANE is basalt erupted on the seafloor and oceanic islands that were accreted (added) to North America during plate convergence.
Erosion of the Coastal Mountains
The Coastal Ranges receive large amounts of precipitation from the stormy North Pacific Ocean. Glaciers and rivers rapidly erode the mountains as they are uplifted.
Temperate Rainforests in Olympic
The highest annual precipitation in the lower 48 nourishes Olympic National Parks northwest side with high slopes, 60 active glaciers and temperate rainforests (~150 in. rainfall/year). Erosion is rapid as a result of this climate. Rainforests Moss hangs from pine branches in the Hoh Rain Forest in Olympic National Park. The northeastern slopes in the rain shadow and are dry in contrast.
Crescent Terrane Basalt
The rocks in this photograph are pillow basalts exposed along the Hurricane Ridge Road. Basalt "pillows" form when lava cools quickly under water. The lack of bubbles in the lava suggests that the rock crystallize
OLYMPIC Convergent Margin of Western North America
The western margin of North America has two parallel mountain ranges due to both active and inactive subduction of oceanic lithosphere.
Lahar
Volcanic mudflow deposits from Mt. Rainier Normal flow of muddy water along the Nisqually River A lahar event would swell the river with a fast-moving, mud and rock-laden slurry
Mt Olympus at 7965' above sea level with the Hoh Glacier.
West Cameron Glacier and moraine sediment. Grooved boulders in the foreground were polished by a larger glacier during the last ice age.
Lava platform on West Side of Lake in Crater Lake
Wizard Island, lava dome, pillow lavas Tongue of lava, cinder cone, wizard island (volcanic cinder cone) The multicolored walls surrounding the lake rise 500 to 2,000 ft above the water, and record the intense volcanic and glacial activity during Mt. Mazama's construction and destruction 7,700 years ago
Coast Ranges
accreted oceanic rocks Olympic National Park, Washington
Turbidites:
deep ocean sedimentary layers of sandstone and mudstone Turbidite Layers: -sandstones deposited in one day during a storm or earthquake -mudstones deposited slowly over hundreds of years
Ash
hot glass from quenched magma bubble walls, crystals, and gasses. The erupted magma was dacite with a SiO2 (silica) content of about 65%. Not composed of dust fragments
CORE AREA
includes the high peaks of the Olympic Mountains (note similar height of the peaks) Bedded sandstone and slate in the Core Area of the Olympic Mountains: The sedimentary layers were metamorphosed and folded vertically before being uplifted above sea level.
