Midterm Exam 2 Review

Near land, what is the speed of a tsunami?

45km/hr (~28mi/hr) which is too fast to outrun but not as fast as in the open ocean

What are the global consequences of giant flood basalts?

Climatic cooling from volcanic aerosols in the upper atmosphere which effect the flux of solar energy reaching earth's surface, and the huge volume of sulfur-rich magma brings natural pollution to deathly levels and could cause mass extinction

Which earthquakes can and cannot cause a tsunami?

Generally it takes an earthquake of M 7.5 or greater to create enough displacement to generate a tsunami. Earthquakes that push land mainly in the horizontal direction are less likely to cause the devastating waves because the land does not raise or lower the water above it enough to cause a tsunami. A a strike-slip fault on land CANNOT cause a tsunami. Tsunamis are mostly caused by earthquakes that occur on the sea floor.

Why was the Toba eruption historically so significant?

a massive volcanic eruption changed the course of human history by severely reducing the human population.

About how many volcano-related deaths have occurred in the past 500 years?

about 278,000 fatalities

What is the height of the initial tsunami waves, immediately following the split into local and distant tsunami waves?

about one-half of that of the original dome of water

How do subduction zone earthquakes cause tsunamis?

by causing the seafloor to move, the upward or downward movement of the seafloor displaces the entire mass of water from the sea bottom to the ocean surface creating potential energy that drives the horizontal movement of the waves, when the uplifted dome of water collapses downward it expands radially splitting into two waves; distant, which travels out across the deep ocean at a high speed, and local which heads in the opposite direction toward nearby land and can arrive quickly following an earthquake with little or no warning time. The height of the initial waves after the split is about one-half of that of the original dome of water.

How do we know about past tsunamis?

by geological investigations which examines the plant material in soil by radioactive dating to determine when they were last alive and associating them with an earthquake that occurred around the same time.

How is the extent and activity of the magma chamber under Yellowstone explored?

by seismic and GPS networks. Also by monitoring ground deformation.

Why does subduction lead to volcanism?

When subducting plates are forced downward into the hotter mantle, volatiles, which are chemical compounds that help break chemical bonds within minerals, are free to rise upward into the formerly dry asthenosphere, causing magma to form due to a lowering of the mantle melting temperature. These subduction zones are responsible for the volcanism on "Ring of Fire."

What is the Volcano Explosivity Index (VEI) scale?

is a quantitative way of evaluating a volcano's eruption. EXPLOSIVITY is measured based on the height of the eruption plume and the VOLUME of ejected material, as well as the overall VIOLENCE of the eruption. With the exception of VEI 0 through VEI 2, the scale is logarithmic, with each interval representing a tenfold increase in the volume of ejected material.

What is the spacing between crests of tsunami waves and the height of the waves in the deep ocean?

spacing between crests = 100km (~ 60 mi) the height of the waves = less than 1m (~ 3 ft.)

What are the factors that influence whether a volcano will explode?

the volatile content and viscosity

How do calderas form?

they form due to a collapse of the land surface or volcanic edifice following partial emptying of the magma chamber. 1) pyroclastic eruption of plume 2) magma chamber drains during voluminous eruption of pyroclastic debris 3) eruptions occur along new fractures and roof of magma chamber begins to collapse 4) pyroclastic deposits build up on the sides and a caldera is formed

How do the Hawaiian Islands generate tsunamis?

they generate tsunamis by the collapse of the chain's massive volcanoes creating massive landslides, thus generating tsunamis. It can be linked to climate change.

What is viscosity a measure of?

viscosity is the resistance to flow in fluids. Fluids that do not flow easily (such as silica-rich felsic magma), have a high viscosity. Fluids that flow readily (such as low-silica mafic magma), have a low viscosity. Example: As magma with a low-silica content and low viscosity erupts onto the earth's surface and flows down the flank of the volcano, the temp cools and the viscosity increases, causing the flow to move more slowly and change in form. The variability in magma viscosity influences both the MOBILITY of the magma under the surface and the FORM it takes when it reaches the surface as lava. The differences in viscosity affect the SHAPE of the volcano, caused by different lava types, and the volatile CONTENT of the magma, which effects the types of volcanic eruptions (peaceful vs. explosive).

About how many total people have been killed by historic tsunamis?

~309,471 people

What are the various causes of tsunamis and which regions of the US do they endanger?

* Coasts near the proximity to a major subduction zone, or directly across the ocean basin from a major subduction zone, are at greater risk. * A major subduction zone is considered to be capable of periodically generating a major earthquake of M 9 or greater. *A locked fault can cause tsunamis, because there is no displacement along the interface of the two plates during an earthquake, the plates must deform elastically causing the ocean floor to uplift triggering a tsunami. *The greatest tsunami hazards are adjacent to those major subduction zones with a convergence of a few cm per year. The two regions of the US that are endangered by tsunamis are Hawaii and Alaska.

What are the indicators that a tsunami wave may be approaching?

* detection of an earthquake in an offshore area that is large enough to produce a tsunami (M 7.0-7.5 or greater) * strong ground shaking on the coast from an earthquake *a noticeable rapid rise or fall in coastal waters. Example: water receding quickly and unexpectedly *an abnormally huge wave *loud ocean roar

What are some basic facts about the Hawaiian Islands?

*Hawaii is the most active and largest shield volcano on earth *the passive behavior of the hawaiian-type eruptions encourages tourists to flock to the island to see lava flowing from the surface.

What are the common precursors to a volcanic eruption and are volcanic eruptions predictable?

*changes in seismic activity- earthquakes may provide the earliest warning of an impending volcanic eruption *changes in local thermal, magnetic, hyrdologic and geochemical conditions *ground deformation (swelling of the ground)- can be detected by satellite-based radar and a network of GPS satellite receivers *increase emission of heat and gas- and changes in chemical composition of gas emissions such as changes in carbon dioxide and sulfur dioxide * Geologic History of a volcano YES, volcanic eruptions are predictable

What are the 3 ways hot rocks melt and where do these processes occur?

1) Decompressing melting- occurs when the rocks are close to their melting temp and the overlying pressure within the asthenosphere is decreased, magma will begin to form even if the temp remains the same. The melting temp for mantle rocks at Earth's surface is ~ 1200ºC. This occurs at locations where the lithosphere is stretched or extended, for example 3/4 of all lava is extruded from undersea mid-ocean ridges (divergent plate boundaries). It also occurs at "hot spots" where a plume of superheated rock rises from deep within the mantle toward the surface. 2) Addition of volatiles- lowers the melting temp of rocks, which are close to their melting temp, by helping to break chemical bonds within minerals thus causing the rocks to begin to melt. Volatiles are chemical compounds such as water, carbon dioxide and sulfur dioxide, which evaporate easily and exist in a gaseous state at Earth's surface. This occurs at subduction zones and is responsible for the "ring of fire." - Volatiles trapped in the minerals in seafloor and in the minerals in oceanic lithosphere, are released as the subducting oceanic plate is forced downward into the hotter mantle, the free volatiles then rise into the dry asthenosphere, lowering the melting temp and melting the rock. 3) Addition of heat- will induce melting if the temp exceeds the melting temp of the rocks at that depth. The movement of heat from high temp areas to low temp areas is caused by the movement of magma within the mantle and ultimately through the crust. This heat causes cooler and shallower rocks (which are close to their melting temp) to melt, forming new magma and becoming mixed with rising magma. This occurrence is widespread. However, hotspots beneath continents can cause the development of large magma chambers. But more importantly crustal assimilation (crustal melting and magma mixing )can occur at hotspots which can have an effect of the type and behavior of the volcano.

What are the eight types of eruptions and their relative sizes?

1) PLINIAN-TYPE ERUPTIONS- explosive eruptions of stratovolcanoes which occur at subduction zones, where volatile-rich basaltic melt rises from the asthenosphere. The HIGH-SILICA content and HIGH VOLATILE content, makes the eruptions EXTREMELY EXPLOSIVE and creates effusive lava flows and pyroclastic debris, that rains down after an eruption. These eruptions are common within the Ring of Fire, and are responsible for more than 80% of the volcanic eruptions, and for most of the death and destruction caused by volcanoes in history. These eruptions have a VEI ranging from 4 to 7. 2) PELEAN-TYPE ERUPTIONS- eruptions of lava domes or stratovolcanoes characterized by highly viscous felsic magma and common along the ring of fire. Although, lava domes are smaller and have LOW to MODERATE VOLATILE content, the HIGH VISCOSITY of the magma means the eruptions can be EXPLOSIVE. Collapse of a growing lava dome can lead to explosive release of trapped volatiles, large destructive volcanic avalanches, as well as, tremendous horizontal blasts that effect large areas. These eruptions have a VEI of 3 to 4. 3) HAWAIIAN TYPE- effusive eruptions such as the ones that build shield volcanoes. They are most common at hot spots, divergent plate boundaries and continental rifts where decompression melting occurs. The LOW-SILICA content and ABSENCE OF VOLATILES during magma formation cause these volcanoes to erupt EFFUSIVELY. VEI or 0 to 1. 4) ICELANDIC- TYPE- effusive eruption from an elongate fissure rather than from a central vent. typically smaller eruptions characterized by a broad and flat upland surface which occur on the flanks of shield volcanoes. VEI of 0 to 1. 5) VULCANIAN-TYPE- basaltic eruptions which can be EXPLOSIVE when magma comes in contact with groundwater, snow or ice, causing large stream blasts creating pyroclastic debris that may rise ~ 6.2 mi into the atmosphere. Can have a VEI as high as 3. 6) STROMBOLIAN-TYPE- basaltic eruptions with INTERMEDIATE EXPLOSIVITY. More explosive than Hawaiian-type eruptions due to a higher volatile content but have similar lava flows. 7) ULTRA-PLINIAN type- the largest, most violent eruptions, which form calderas due to collapse of land surface or volcanic edifice following partial emptying of magma chamber. These eruptions may explosively extrude more than 100km^3 (~ 62 mi^3 ) of pyroclastic debris, consisting mostly of ash. 8) SUPER-VOLCANIC TYPE- the largest caldera eruptions in which the magma has a very high volatile content and high silica content suggesting that melted continental crust has mixed with the magma and must rise through thick felsic crust, such as when a hot spot is located beneath continental lithosphere.

What is the four stage process that leads to tsunami waves on the shore?

1) an earthquake rupture uplifts the seafloor and the water surface thats uplifted creates an elongated dome parallel to the fault that collapses and generates a tsunami wave. Additional waves can be produced by oscillations of the water surface and aftershocks which radiate outward. 2) In the deep ocean, tsunami waves move very rapidly and are spaced long distances apart. 3) As tsunamis approach land, the water depth decreases therefore the velocity of the tsunami decreases and spacing between wave crests decreases (the wavelength). Since the water slows and piles up the height of the waves increases. 4) When the first tsunami reaches the shore it may be several meters to several tens of meters high and destroys everything in its path. Sometimes the trough wave arrives first, exposing the seafloor. They generally don't arrive as giant breaking waves, when they arrive they usually arrive as a very strong, fast-rising increase in sea level. On the rare occasion that tsunami waves break they appear as a vertical wall of turbulent water. The movement of a tsunami inland is called the runup of the wave, and refers to the furthest horizontal and vertical distance that the largest wave of a tsunami moves inland. Once it moves the farthest inland that it can, the water then returns to the open ocean in a strong turbulent flow. Edge waves can can also be generated by tsunamis, which are waves that travel back and forth parallel to the shore. The interaction of edge waves and tsunami waves can cause amplification of second or third tsunami waves and this serious of waves will strike a particular coast over a period of several hours

How does the DART tsunami early warning system work?

A DART system consists of three parts; 1) A network of seismographs to accurately locate and determine the depth and magnitude of submarine and costal earth quakes. This is also known as a seafloor bottom pressure recording (BPR) system. 2) Automated tidal gauges to measure unusual rises and falls of sea level. 3) A network of sensors known as "tsunameters" are connected to floating buoys which detect small changes in the pressure exerted by the increased volume of water as a tsunami passes overhead. the buoys detect small changes in the pressure from bottom-pressure recorders on the seafloor and this information is relayed to the buoy along with readings from surface weather instruments and sends the information to a satellite which then relays the information to a warning center and this information is combined with tidal gauge information to predict tsunami arrival times.

How do tsunami and wind-blown waves differ?

A tsunami is caused by a massive disturbance to a large body of water and surf waves are formed by wind which imparts energy to the water surface, forming waves. Tsunamis travel very fast (several hundreds of kms per hour). They are about 10 times faster than a wind-generated wave. (~50 km per hour) Tsunamis have very long wavelengths (over 100 km). Ocean swells are about a thousand times shorter - they have wavelengths about 150 m at the most. Tsunami waves travel through the whole water column down to the sea floor, even to depths of thousands of meters. Ocean swells are surface waves and do not 'feel' the sea floor, except in shallow water. Surf waves form a whitecap and often have an unbroken front face of water before breaking. A tsunami usually doesn't break but instead surges onto land. Even if it does break, it doesn't look like a surf wave, it forms a turbulent bore, which is a surge of white water without a clear face.

Why do geysers erupt but hot springs do not?

Geysers require 3 elements to form; 1) water supply 2) heat source 3) proper underground water circulation system Hot springs only consist of a water supply and heat source therefore they can not erupt. Geysers, however, have a water supply and heat source, like a hot spring, but also have an underground plumbing system that allows water to heat up as it fills underground reservoirs and when the pipe that leads to the surface, where the steam bubbles rise, constricts, the pressure begins to build until the pressure is to great and the water shoots out of the the surface in tall columns. Sometimes this constriction does not occur in the pipes, causing the geyser eruptions to be smaller because there is no build up of pressure.

What was Pliny the Younger famous for?

He was famous for his collection of letters some of which survived the destruction at Pompeii making possible the social reconstruction of an age for which there is otherwise no serious historical record.

What is the cause of hotspot volcanism and why does it lead to a chain of volcanoes?

Hot spots are INTRAPLATE REGIONS of voluminous volcanism caused by large plumes of anomalously hot mantle which are generated in the lower mantle and rise by convection, once it reaches the base of the lithosphere, it spreads outward into a mushroom shape. DECOMPRESSIONAL MELTING of this hot mantle source can generate huge volumes of basalt magma creating what is referred to as a hot spot. As lithospheric plates move across stationary hotspots, volcanism will generate volcanic islands that are active above the mantle plume, but become inactive and progressively older as they move away from the mantle plume in the direction of plate movement. Thus, a linear belt of inactive volcanic islands and seamounts will be produced.

How do the characteristics of a tsunami wave change as a function of water depth?

In the deep ocean tsunami waves move more rapidly and are spaced long distances apart. As the water depth decreases and the waves approach the shore the velocity decreases (forward speed) and since the velocity decreases the spacing between crests (wavelength) decreases. As the water slows, it piles up and the height of the tsunami wave increases.

What are the basic characteristics of the various volcanic hazards (primary and secondary) and which ones cause the most and least fatalities?

PRIMARY EFFECTS: • Lava Flows; when magma reaches the surface and overflows the central crater or erupts from a volcanic vent along the flank of a volcano • Release of Volcanic Gases- poisonous gases • Pyroclastic Activity; explosive volcanism in which magma and the rocks that compose the volcano are physically blasted from a volcanic vent into atmosphere - tephra- pyroclastic debris - pyroclastic debris- accumulation of tephra - Ash fall: volcanic ash develops due to explosive fragmentation of magma during an eruption and occurs downwind of the volcano as the particles cool and fall, this destroys vegetation, contaminates surface water, causes structural damage, health hazards and effects aviation -pyroclastic flow: (most LETHAL aspect of volcanic eruptions) very hot flows of pyroclastic debris which races down the volcano incinerating any organic mater. SECONDARY EFFECTS- • debris flows- fast-moving mixtures of fine sediment and large rocks that have a consistency similar to wet concrete. • mudflows- mudflows which originate on the flanks of volcanoes • landslides or debris avalanches- can effect areas far from their source and can trigger tsunamis • floods • fires • global cooling of the atmosphere for a year or so.

What is the history, evidence for, and the consequences of large, explosive eruptions at Yellowstone?

The explosion 640,000 years ago at yellowstone national park is one of the best-known caldera-forming eruptions which blanketed large parts of North America in ash and devastated the U.S. economy, food production, capabilities and had negative impacts on global climate change. The eruptions have left yellowstone with hot springs and geysers. This site is still capable of producing volcanic activity because magma is still present at shallow depths beneath the caldera floor and this is shown because its floor has domed upward since the last eruption.

How do shield volcanoes, stratovolcanoes, and cinder cones form?

The type of volcano that forms is the result of HOW and WHERE the magma formed, the amount of magma evolution (silica enrichment (viscosity)) that occurred on the way to the surface, and the volatile content of the melt. SHIELD VOLCANO- the largest volcanoes, constructed from balsaltic lavas, forming a gentle arch or shield shaped volcano with shallow slopes built up from many lava flows which cover a large region due to their low viscosity. STRATOVOLCANO- is composed of andesite, forming a cone shaped volcano with steep sides caused from build up from lava flows, due to a high viscosity; causing the lava to not travel far, and the build up of pyroclastic deposits. CINDER CONES- are formed by the accumulation of tephra (rock fragments and particles ejected by a volcanic eruption, in particular volcanic rock known as Scoria) near a volcanic vent. Which forms a cone shaped volcano with deep sides and a summit crater.

What is the velocity of a tsunami wave in the deep ocean?

Their velocity is equal to the square root of the product of the acceleration of gravity and the water depth. acceleration of gravity - 10m/sec^2 average water depth- 4000m √((10m/sec^2)*(4000m))= 200m/sec 200m/sec = 720km/hr (close to the average airspeed of a jetliner)

Why did so many people die around the Indian ocean due to the 2004 tsunami?

There was no warning system in place, therefore, the residents of costal areas were struck by a series of tsunami waves without warning. The source of the tsunami was the world's largest earthquake in the past four decades. Because of the large amount of displacement this was classified as a "mega-thrust event." Warnings from a center in Hawaii did not reach regions surrounding the Indian Ocean in time to take action and even if it did there was no protocol to notifying costal residents. More than 3/4 of the deaths were from intense shaking from the earthquake and the flooding caused by tsunami waves within the first hour.

What is the history of large Yellowstone eruptions?

Three extremely large explosive eruptions have occurred at Yellowstone in the past 2.1 million years. Tiny particles of volcanic debris (volcanic ash) covered much of the western half of North America, likely a third of a meter deep several hundred kilometers from Yellowstone and several centimeters thick farther away. Wind carried sulfur aerosol and the lightest ash particles around the planet and likely caused a notable decrease in temperatures around the globe.

Why is the destruction of Pompeii in 79 AD so interesting?

Usually, the eruption column which is loaded with pyroclastic debris is supposed to be carried upward by hot expanding gases even though the debris is denser than the surrounding atmosphere. However, in Pompeii, the increase in density of the pyroclastic debris or decrease in the upward thrust of gases caused the eruption column to collapse in multiple instances, forming a flow of hot pyroclastic material down the eruption column and flank of the volcano. Thus burying the towns of Pompeii and Herculaneum in pyroclastic debris.

What are the settings where the different types of volcanism are found and what does the Ring of Fire refer to?

Volcanism is typically related to plate tectonics because spreading or sinking plates at boundaries interact with other earth materials to produce molten rock, magma, within the earth, or lava when it erupts onto the earth's surface. Most volcanoes are located near active plate boundaries. About 2/3 of all active volcanoes are located on the Pacific "Ring of Fire" (surrounding the Pacific Tectonic Plate).

When do water waves generally break?

Waves break when their amplitude reaches a critical level that causes large amounts of wave energy to be transformed into turbulent kinetic energy. When waves reach shallow waters - usually near coastlines - they increase in height, and their crests meet the Law of Gravitation. The waves break. Waves begin to break when the ratio of wave height/wavelength exceeds 1/7. As waves reach the shore, the energy in front of the wave slows down due to friction with the shallow bottom. Meanwhile, the energy behind the wave moves at full speed and is channeled upwards, climbing the back of the bulging wave. The wave breaks, and it usually does so in water depth that is 1.3 times the wave height.

What are the global consequences of large volcanic eruptions?

large volcanic eruptions can create a cloud of aerosols and ash in the stratosphere causing global cooling due to the scattering of sunlight, ultimately leading to crop failures, famine and disease.

What are the dangers tsunamis pose when they come on shore?

major flooding which can destroy boats, buildings, bridges, cars, trees, telephone lines, power lines - and just about anything else in their way. Can also result in massive loss of life. also results in erosion; tearing up beaches, costal vegetation, homes and buildings. Debris is carried by the water inland and then back out again to the ocean leaving bare, eroded ground and other areas covered with human and natural debris. Secondary effects of tsunamis occurs in the hours, days and weeks following the event including; fires, polluted water supplies and disease.