5-1 ASSIGNMENT:
EARTHQUAKES
AND VOLCANOES
Laura Spradley
Southern New Hampshire University
PHY103: Earth System Science
Lynda Folts
November 27,2022
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5 - 1 ASSIGNMENT:
EARTHQUAKES
AND VOLCANOES
Laura Spradley
Southern New Hampshire University
PHY103: Earth System Science
Lynda Folts
November 27,
EARTHQUAKES: WHAT ARE THEY?
HOW THEY OCCUR?
AND HOW FREQUENTLY THEY
OCCUR ON A GLOBAL BASIS.
Earthquakes are any sudden earth trembling brought on by seismic
waves moving through the Earth's rocks. Earthquakes most
frequently occur along geologic faults, which are narrow zones
where rock masses move in relation to one another. Seismic waves
are produced when some type of energy stored in the Earth's crust
is suddenly released, typically when masses of rock straining against
one another suddenly fracture and "slip." The largest tectonic plates
that make up the crust of the Earth are where most of the world's
major fault lines are found. Around the world, there are an average
of 20,000 earthquakes every year, or 50 per day, according to the
National Earthquake Information Center (NEIC). However, it is
predicted that there are millions of earthquakes each year that are
too small to be noticed. There are frequent earthquakes all around
the planet. Globally, there may be 20 to 25 earthquakes of
magnitude 7 on average each year, or one every two to three weeks.
On the other end of the magnitude spectrum, there are literally
millions of little earthquakes each year throughout the planet.
Slide A 2
This Photo by Unknown author is licensed under CC BY.
EARTHQUAKE INTENSITY VS EARTHQUAKE
MAGNITUDE
Intensity
However, intensity reflects the level of shaking brought on by an earthquake at a specific location and diminishes with distance from the epicenter. For instance, intensity levels of 1 (not sensed), 2 (barely noticeable), 3 (weak, only felt by a few), and 12 (complete devastation) are awarded. For the study of earthquakes that happened before the development of instrumentation for monitoring, the analysis of intensity and the creation of isoseismic maps, which outline areas of identical intensity, are crucial. The Modified Mercalli Intensity Scale is a descriptive scale that is used to determine the intensity of an earthquake's shaking.
Magnitude
The magnitude of an earthquake refers to its size. Each earthquake has its own magnitude. The magnitude scale, which measures an earthquake's size, is unaffected by distance from the event. Thus, we can discuss a magnitude 5.4 ML event that had an intensity of 6 EMS at the epicentral region on the Lleyn Peninsula but an intensity of 3 EMS at Carlisle. Instrumental monitoring is necessary for the calculation of magnitude. Magnitude: The size of an earthquake is a numerical indicator of the magnitude of the earthquake at its source. The Richter Magnitude Scale gauges the seismic energy that an earthquake releases.
Slide C
TYPES OF FAULTS
Normal (extensional) faults, reverse or thrust (compressional) faults, and strike-slip (shearing) faults are among the several types of faults. Normal Fault: Blocks above and below an angled fault migrate downward in relation to one another. Tensional forces are what drive this fault motion, which extends. [Other names include gravity fault, normal-slip fault, and tensional fault] Basin and Range faults are one example. Reverse Fault: In relation to the block below the fault, the block above the inclined fault rises. Shortening arises from this fault motion, which is brought on by compressional stresses. If the fault plane's dip is minimal, a reverse fault is referred to as a thrust fault. [Other names: compressional fault or reverse-slip fault.] The Rocky Mountains and the Himalayan Mountains are two examples. Strike-slip Fault: Blocks move horizontally along a fault, and the fault plane is almost vertical. The fault is referred to as left-lateral if the block on the far side of the fault shifts to the left, as seen in this animation. The fault is referred to as right-lateral if it shifts to the right. Shearing forces are what create the fault motion on a strike-slip fault. [Other names are wrench fault, tear fault, lateral fault, and trans current fault.] Examples include the Anatolian Fault in Turkey and the San Andreas Fault in California.
Slide D
THE MOST POWERFUL EARTHQUAKE IN THE UNITED
STATES
On March 28, 1964, an earthquake with a magnitude of 9.2 was measured near Prince William Sound,
Alaska, and it was the most severe to ever hit the United States. Only 139 people were killed in the
earthquake, far fewer than in several of the deadliest earthquakes ever. Alaska, Arkansas, California,
Hawaii, Idaho, Illinois, Kentucky, Missouri, Montana, Nevada, Oregon, South Carolina, Tennessee, Utah,
Washington, and Wyoming are the 16 states with the highest seismic threat from natural earthquakes.
Slide F
TYPES OF FAULTS AND POTENTIAL THREATS
A fault is a flat rock fracture when there has been movement-related displacement. Large-scale faults are
caused by crustal movement brought on by plate tectonic activity. Most earthquakes are caused by an
energy release linked to rapid movement along active faults. The numerous tectonic plates that make up
the Earth's outer shell are constantly moving, and this movement is what causes the majority of
earthquakes, tsunamis, landslides, and volcanic eruptions that occur around the world. Subduction zones,
where two plates clash and one is shoved beneath the other, are where these natural disasters with the
greatest destructive power occur.
Slide G
EARTHQUAKE IN MY CURRENT LOCATION (NORTH
CAROLINA, USA)
After two earthquakes with magnitudes of around 2 were detected 50 miles northwest of Charlotte within
a week in May 2022, a magnitude 1.8 earthquake with the same magnitude was observed near Lake
Norman in the middle of August. Henri Gavin, a professor at Duke and an expert in seismic engineering,
reported Monday that there had been three minor earthquakes in western North Carolina over the
previous week. An average of one of these earthquakes occurred every two weeks in 2021, or around 30 in
total. The likelihood of three earthquakes occurring in one week is roughly 15%, assuming 2021 was a
typical year for such events. Like rolling two six-sided dice and getting a seven, roughly. According to the
U.S. Geological Survey, South Carolina has been experiencing a "swarm" of earthquakes, which are defined
as "a sustained sequence of earthquakes without any identifiable principal event or mainshock." According
to the USGS, a magnitude 3.6 earthquake in late June was the greatest linked earthquake to far.
Slide I
VOLCANOES
Laura Spradley
Southern New Hampshire University
PHY103: Earth System Science
Lynda Folts
November 27,
This Photo by Unknown author is licensed under CC BY-SA.
TYPES OF VOLCANOES
Cinder Cones: Volcanoes with cinder cones are the most basic. They are created from cinder, or tiny chunks of solid lava, which are released from vents. As magma emerges from the Earth, the ground trembles. Then comes a huge explosion that sends molten rocks, ash, and gas flying into the air. The rocks pile up aro und the vent as they crash to the ground after rapidly cooling in the air and falling to the surface of the earth. They build up into a little cone of cinder that can rise to a thousand feet abov e the surrounding terrain. If there is wind present at the time of the eruption, the cinder is first carried downwind before being deposited in an oval pattern. Lava flows that extend outward from the eruptive vent are fed by the same eruptions that create cinder cones. The bowl-shaped crater designating the vent may typically be found when climbing a cinder cone. If cinder and lava flows erupt from the same vent repeatedly, the overlapping layers may eventually coalesce to produce a composite volcano (stratovolcano). On a map, you can see that western North America and other volcanic regions throughout the world are home to thousands of cinder cones. Composite Volcano (Stratovolcano): Compound volcanoes, also known as stratovolcanoes, are responsible for some of the world's largest mountains. They are often constructed of recurrent layers of lava flows, volcanic ash, cinders, boulders, and volcanic bombs, and have steep, even sides. Some composite volcano es reach heights of more than 8,000 feet above the ground, but when compared to the sea, they are considerably higher (called above sea level). The tallest volcano in the United States is Mount Rainier in Washington State, which has a peak elevation of 14,410 feet. The tallest composite volcano on Earth is Ojos del Salado in Chile, which has a summit elevation (height above s ea level) of 22,615 feet. The world's most renowned and stunning mountains, such as Mount Fuji in Japan, Mount Cotopaxi in Ecuador, Mount Shasta in California, Mount Hood in Oregon, and Moun t St. Helens in Washington, are all composite volcanoes. Shield Volcano: Volcanoes that form shields are mostly made of flowing lava. Lava spews from vents in all directions, either along two to thr ee rift zones (fractures) that extend forth from the summit like spokes on a bicycle wheel, or from the summit itself (top). Lava flows build up a broad, gently sloping dome form that resembles a warrior's shield from a distance when they cross each other. Shield volcanoes gradually form because of the formation of countless lava flows that spread widely over vast dis tances before cooling as thin sheets. Shield volcanoes are some of the largest volcanoes on Earth. Many shield volcanoes in northern California and Oregon are up to 3 or 4 miles broad and as tall as 1,500 to 2,000 feet. A line of shield volcanoes, including Kilauea and Mauna Loa, the largest active volcano in the world, make up the Hawaiian Islands. When viewing photographs of vol canoes, you can typically tell if they are shield volcanoes or stratovolcanoes based on their shape. Lava Dome: Lava domes technically aren't of the "volcano type," but rather an eruption occurrence because a volcano can support numerouslava domes over an extended period of time. Lava flows that are too thick to flow away from the vent are what are known as lava domes. A massive pile of lava forms over and a round the vent as lava squeezes out of it. Some domes resemble sharp spines, while others have the appearance of a big muffin, opening flower petals, or tongues or flows with steep sides. On the sides of enormous composite volcanoes with steep sides or within craters, lava domes frequently form. Lava domes may pose a threat. They mainly expand from within as they grow. The cooler, harder outer surface breaks when new magma fills the interior, spewing hot rock and gas down the mountainside. The Alaskan Katmai Volcano's 1912 eruption created the circle-shaped Novarupta Dome, which is 800 feet across and 200 feet high. One of the final lava squirts to emerge from a much larger and protracted eruption was this dome. The greatest and most destr uctive eruption to ever take place in the United States was that at Katmai.
Slide K
PICTURES OF THE DIFFERENT TYPES OF VOLCANOES
Composite Volcano
(Stratovolcano)
This Photo by Unknown author is licensed under CC
Lava Dome Shield Volcano
Cinder Cone
VOLCANIC HAZARDS
Volcanic Earthquakes: Volcanic activity-related earthquakes can result in risks such ground fissures, ground deformation, and damage to buildings. Long period earthquakes and volcano-tectonic earthquakes are the two main types of earthquakes that can happen at a volcano. Volcano-tectonic earthquakes are caused by stress changes in solid rock because of the injection or withdrawal of magma (molten rock) (Chouet, 1993). Large ground fissures and land subsidence are both possible effects of these earthquakes. These earthquakes might happen as rock fills in the voids left by the absence of magma. Volcano-tectonic earthquakes can happen at any moment; they are not a sign that the volcano will erupt. Long-period earthquakes, which are caused by the injection of magma into the surrounding rock, are the second type of volcanic earthquake. As the magma is transported unevenly, pressure variations cause these earthquakes. When magma injection continues, several earthquakes are caused (Chouet, 1993). Such behavior is a sign that a volcano is about to erupt. Seismographs are used by scientists to capture the earthquake signal. Volcanic tremor is the name of this signal. Directed Blasts: In a typical volcanic eruption, pyroclastic material is thrown into the atmosphere in the form of an eruption column. The gas thrust zone at the bottom of this column is where material is launched ballistically from the volcanic vent. The convective thrust zone is located above this z one. Pyroclasts are buoyed upward toward the top of the troposphere in this region by heat. Shearing takes place once the eruption column reaches the stratosphere, and the material is then dispersed in the form of an umbrella (Francis, 1993). Tephra: Sometimes when a volcano erupts, it will hurl debris into the air, like pieces of rock. Tephra is the name for this substance. Blocks and bombs are the names for the tephra that is the largest (more than 64 mm). Usually, the volcano shoots blocks and bombs ballistically. These particles bre ak out close to their source because they are so massive. Blocks and bombs up to 8-30 tons have detonated up to 1 km away from their source (Bryant, 1991). Small bombs and blocks have been known to fly up to 80 kilometers (Scott, 1989) away! Some of these bombs and blocks have speeds between 75 and 200 m/s (Bryant, 1991). Volcanic Gases: Tephra, gases, and heat are all released into the atmosphere during a volcanic eruption. Water vapor makes up the majority of gases that are emitted into the atmosphere. Other gases include carbon monoxide (CO), hydrogen gas (H2), NH3, methane (CH4), sulfur dioxide (SO2), hydrochloric acid (HCl), hydrogen fluoride (HF), hydrogen sulfide (H2S), carbon dioxide (CO), hydrogen gas (H2), and silicon fluoride (SiF4). While some of these gases condense into salts and aerosols, others are carried away from the eruption on ash particles. Additionally, volcanic gases are created when magma heats water. Additionally, gases can be released via pyroclastic flows, lahars, and lava flows, as well as from burning vegetation. High amounts of these gases can leak out of the atmosphere and cause acid rain. Lava Flows: The least dangerous process involved in volcanic eruptions is lava flow. The temperature, silica content, extrusion rate, and slope of the terrain are all factors that affect how far a lava flow travels. A lava flow with a high silica content or one that is chilly will not move very far. Such a flow would be extremely viscous (a high resistance to flow). Low silica concentration and low viscosities allow basalt flows, such those in Hawai'i, to flow over great distances.
Slide M
VOLCANIC HAZARDS PT.
Debris Avalanches, Landslides, and Tsunamis: When an unstable slope gives way and debris is thrown off the slope, a debris avalanche is created. Normally, particularly steep volcanoes have large-scale avalanches. There are two main categories of debris avalanches: "cold" and "hot" avalanches. A slope becoming unstable usually creates a cold debris avalanche, whereas volcanic activity, such as volcanic earthquakes or the injection of magma, results in a hot debris avalanche. Mass movement is referred to as a landslide in general. Instead of the more abrupt action of an avalanche, it suggests a steady progression. On the south side of the island of Hawaii, there is a wonderful illustration of potential large-scale land sliding that is already occurring. Avalanches and landslides can result in a variety of dangers. Both processes can cover great distances and obliterating everything in their path. They can dam lakes and rivers, causing flooding. A volcanic eruption could also be brought on by a landslide or avalanche that results in a drop in pressure. People who live in valley regions distant from the volcano's summit may be affected by lahars, which are created when water and debris from an avalanche or landslide combine. Large sea waves with lengthy wave durations are known as tsunamis. These waves can travel a great distance inland once they reach the coast. Pyroclastic Surge: Low density flows of pyroclastic material are known as pyroclastic surges. They have a low concentration of particles and arerich in gases, which accounts for their low density. These currents move quickly and are quite erratic. Pyroclastic Flows: In response to gravity, fluidized masses of rock pieces and gases called pyroclastic flows move quickly. Pyroclastic flows can develop in a variety of ways. They may develop as a result of the explosion or gravity collapse of a lava dome or lava flow, as well as when an eruption co lumn collapses. Lahars: Lahars resemble pyroclastic flows but have more water in them. Lahars are formed in five different ways:
- by debris avalanches, which contain water from snow and ice that, when released, mixes with loose debris to form a lahar
- by pyroclastic flows and surges, which also release water that mixes with debris
- by pyroclastic flows, which dilution with river water as they travel downslope
- by natural dam failure (such as a lava flow dam or crater lake) 5)Lahars with a 20–60% sediment content are typically quite turbulent.