Chapter 6 Volcanoes. Volcanoes & Plate Tectonics Volcanic Activity Volcanoes in Idaho??? http://www.youtube.com/watch?v=bgRnVhbfIKQ. Student Objectives.
Volcanoes & Plate Tectonics Volcanic ActivityVolcanoes in Idaho???
What happened to Pompeii preserved a treasury of information about life in the ancient Roman Empire. The ash and lava quickly ended their lives and preserved their day’s activities.These people below died instantly. Their bodies decayed inside the rock and ash tombs. Later, the hollowed areas were filled in with minerals.
There are about 600 active volcanoes on land. Many more lie beneath the sea.
Volcanoes occur in belts that extend across continents and oceans, such as the Ring of Firein the Pacific Ocean.
Volcanoes can be found at
Subductioncauses slabs of ocean crust to be thrust down through a deep-ocean trench into the mantle. The crust melts and forms magma, which rises back toward the surface, erupting as lava.
This is a common sight there!
A hot spot is an area where magma from deep within the mantle melts through the crust like a blow torch. Hot spots often lie in the middle of continental or oceanic plates far from any plate boundaries.
Yellowstone marks a major hot spot. The last major eruption in Yellowstone was 75,000 yearsago.
Juan de Fuca Plate off the coast of Washington state, Oregon, and Vancouver BC
The Juan de Fuca is an interesting area for tectonic research due to several unique characteristics. The Juan de Fuca has all three types of dynamic plate boundaries occurring within a relatively small area.
The Snake River Plain extends 400 miles (650 km) westward from northwest Wyoming to the Idaho-Oregon border. The Snake River Plain is a broad, flat depression, which covers one quarter of the state of Idaho.
The geysers, hot springs, and bubbling mud pots of Yellowstone National Park indicate there is extra heat beneath the northwest corner of Wyoming.
The heat is from a hot spot beneath Yellowstone that causes all the sensational features in Yellowstone.
This hot spot used to be under Idaho!!
Thousands of steaming geysers, shimmering thermal pools, and bubbling mud pots are evidence of this hot spot activity
But the greatest wonder of all goes mostly unnoticed deep beneath Yellowstone!
Hidden underground, powerful volcanic, tectonic, and hydrothermal forces are continually reshaping the landscape of Yellowstone.
Symptoms of the underground turmoil include numerous earthquakes (most too small to be felt), uplift and subsidence of the ground surface, and persistent but ever-changing hydrothermal activity.
Eventually, the unrest will culminate in another large earthquake or volcanic eruption, both of which have occurred many times before in Yellowstone's geologic past.
The largest and most explosive volcanic eruptions eject tens to hundreds of cubic kilometers of magma onto the Earth's surface. When such a large volume of magma is removed from beneath a volcano, the ground subsides or collapses into the emptied space, to form a huge depression called a caldera. Some calderas are more than 25 kilometers in diameter and several kilometers deep.
Craters of the Moon is a volcanic field of old calderas. Craters of the Moon had 8 eruptive episodes from 15,000 to approximately 2,000 years ago.
Craters of the Moon lava field lies along the northern border of the Snake River Plain.
Expanding gases in the lava ejected rocks hundreds of feet into the air.
The tops literally were blown off (and the ash landed in Nebraska and Wyoming) resulting in the Idaho smiley face.
This picture shows how the plate moves over the hot spot producing island arcs. Idaho’s caldera were formed in a similar manner!
Huge calderas of up to 30 miles in diameter were formed when these devastating eruptions took place.
Later a more fluid lava flowed onto the surface and covered the crater, giving it the smoother texture that we see in the satellite photos.
As you drive along the highway in southern Idaho, you are driving through these huge ancient Caldera!
Calderas become progressively younger from west to east. The Yellowstone calderas are the youngest and mark the approximate location of the hotspot.
The lake was formed after the collapse of an ancient volcano, posthumously named Mount Mazama. This volcano violently erupted approximately 7,700 years ago. That eruption was 42 times as powerful as the 1980 eruption of Mt. St. Helens. The basin or caldera was formed after the top 5,000 feet of the volcano collapsed. Subsequent lava flows sealed the bottom, allowing the caldera to fill with approximately 4.6 trillion gallons of water from rainfall and snow melt, to create the seventh deepest lake in the world at 1,932 feet.
Watch all the different kinds of lava flows
Notice how the houses instantly ignite when the lava comes close
Witness what happens to the highway when the lava creeps across
Why do you think the song may be appropriate for the name “Ring of Fire?”
A composite volcano is built by alternating eruptions of lava and pyroclastic material. Composite volcanoes form tall conical mountains. They have both violent and gentle eruptions.
Examples include Mt. Vesuvius & Mt. St. Helens
Mt St Helens in eruption is shown in the this photo. Mt. St. Helens had a nearly perfect symmetrical form previous to the 1980 eruption. This indicates the youth of this volcano. St. Helens was very active during the 19th century but remained quiet until 1980.
Mt Shasta stands nearly as tall as Mt. Rainier and like Mt. Rainier it poses great dangers for the surrounding towns. Mt. Shasta is actually comprised of 4 volcanoes. The modern summit and Shastina on the west flank are easily distinguished in this photo. Shasta has been the source of many large debris avalanches andpyroclastic flows.
Mt Rainier, at 14,410 feet, is the highest of the Cascade volcanoes. This view from the north side shows that Mt. Rainier was once significantly higher. Notice that the lava flows on both the east and west sides project to a much higher summit that was destroyed in an eruption over 4,000 years ago. Also notice the symmetry and youth of the modern summit.
Glacier Peak, in the north central Cascade Mountains, is comprised mainly of lava flows that have erupted in the last 770,000 years. The volcano has been inactive during the last 12,000 years. This view of the north side is from Image Lake.
A shield volcano is gently sloping sides and is typically built by eruptions of fluid basaltic lava that are slow, gentle, and relatively quiet forming many layers.
The Hawaiian Islands are an example of shield volcanoes and are all very broad with gently sloping sides.
Here’s another view comparing the heights of Mt. Everest on the Earth, Maxwell Montes on Venus and Olympus Mons.
Cinder cones are constructed from the deposition of cinders and other pyroclastic material and usually have sudden, violent eruptions. They are formed from layers of ash, cinders, and dust and are a cone shaped mound.
Mt. Paricutin, Mexico is an example of a cinder cone.
Magmais molten rock found beneath the earth's surface. Magma is extruded on to the surface as lava.
Lava flows are streams of molten rock material extruded onto the surface of the earth.
AA – The picture below shows aa type lava flow, Kilauea Volcano, Hawaii
An AA-type lava flow (a Hawaiian term pronounced "ah ah") has a rough, rubbley surface and flows across the surface in a roller-like motion.
Pahoehoe –(pronounced "pah hoy hoy") has a smooth glassy, ropey appearance and advances the across the surface in a series of overlapping lobes.