Hazardous environments Flashcards
What are the human impacts?
Injection of waste fluids in the ground, commonly a byproduct of an extraction process for natural gas known as fracking, can increase the outward pressure that liquid in the pores of a rock exerts, known as pore pressure. The increase in pore pressure decreases the frictional forces that keep rocks from sliding past each other, essentially lubricating fault plane. The largest earthquake induced by fluid injection that has been documented in the scientific literature was a magnitude 5.8 earthquake on September 23, 2016 in central Oklahoma.
Explain how volcanic eruptions cause tsunamis.
(secondary hazards)
Most likely to be cause by a composite volcano.
Volcano tsunamis can result from violent submarine explosions alongside caldera collapses, tectonic movement due to volcanic activity or pyroclastic flows which reach the ocean. All of these factors lead to the displacement of water which is responsible for the creation of the tsunami which spread out from the source.
Approximately 5% of tsunamis are formed from volcanoes and approximately 16.9% of volcanic fatalities occur from tsunamis.
Impacts of a tsunami?
Explain the effect high silica magma on volcanic eruptions.
Magma with high silica content also tend to cause explosive eruptions. Magma with high silica content has a stiff consistency and can harden, blocking the vents of the volcano. These leads to rising magma to build up, leading to an increase in pressure and a more explosive eruption.
-700oC
-Slow moving lava flows.
Describe runny lavas.
The hottest lavas with the lower silica content are quite runny. These are known as basic or basaltic. They are able to travel able to travel long distances even over relief that if relatively gently sloping, before cooling and solidifying as basalt.
Lapilli
Small, pebble like bits of magma that hardened before they heat the ground
Describe and explain the characteristics of pyroclastic flow.
Pyroclastic flow is a fast-moving current of hot gas and volcanic matter that flows along the ground away from the volcano at velocities of 100km/h on average but is capable of reaching speeds of 700km/h.
Common cause is when the column of lava, ash, and gases expelled from a volcano during an eruption loses its upward momentum and falls back to the ground.
They can be extreme destructive as they are extremely hot (over 800 degrees Celsius) and are therefore very mobile.
Occur on composite volcanoes.
The 2018 Volcán de Fuego eruption was an eruption of Volcán de Fuego in Guatemala on Sunday 3 June 2018. The eruption produced a large ash plume fed by continuous explosions, pyroclastic flows, and lahars. Pyroclastic flows descended the Las Lajas ravine and overspilled its confines, causing the death of officially nearly 200 people.
Describe and explain the characteristics of lahars.
Occurs on composite volcanoes
Lahars are volcanic mudflows with the consistency of wet concrete. Lahars form when ash deposits, rock fragments and mud mix with water. The water can originate from heavy rainfall or melting snow and ice on or above a volcano. Lahars can travel at speeds of up 200km/h on a steep slope. and flow distances of more than 300km. Lahars can consumer everything in their path, burying its under layers on debris.
Lahars from the 1985 Nevado del Ruiz eruption in Colombia caused the Armero tragedy, which killed an estimated 23,000 people.
Describe and explain the characteristics of toxic gases.
(primary hazard)
The most common volcanic gas is water vapour, carbon dioxide and sulfur dioxide. Other volcanic gases include hydrogen chloride, carbon monoxide, and hydrogen fluoride
Exposure to acid gases such as sulfur dioxide, hydrogen sulfide, and hydrogen chloride can damage eyes and mucous membranes along with the respiratory system and, under extreme conditions, can lead to death
Rhyolite
Volcanic rock (or lava) that characteristically is light in color, contains 69 or more percent of silica, and is rich in potassium and sodium. Low-silica rhyolite contains 69 to 74 percent silica. Rhyolitic lavas are viscous and tend to form thick blocky lava flows or steep-sided piles of lava called lava domes. Rhyolite magmas tend to erupt explosively, commonly also producing abundant ash and pumice.
Describe the distribution of earthquakes.
Most of the world’s earthquakes occur in clear defined linear patterns which generally follow plate boundaries.
For example, there is a clear line of earthquakes along the centre of the Atlantic Ocean in association with the Mid-Atlantic Ridge (a constructive plate boundary). Similarly, there of earthquakes along the west coast of South America and around the eastern Pacific associated with subduction of the Nazca Plate beneath the South American Plate (a destructive plate boundary).
Broad belts of earthquakes are associated with subduction zones, narrower belts of earthquakes are associated with constructive plate boundaries.
Describe the distribution of volcanoes.
Most volcanoes are found at plate boundaries although there are some exceptions, such as the volcanoes of Hawaii that stretch north-west across the Pacific Ocean, which occur over hotspots. About three quarters of the Earth’s 550 historically active volcanoes lie along the Pacific Ring of Fire. This includes many of the world’s most recent volcanoes, such as Mt Pinatubo in the Philippines, Mt Helens in Washington State, U.S.A. The Pacific Ring of Fire is related to subduction either beneath oceanic or continental crust, the process of subduction forms volcanic island arcs such as the Aleutian Arc where the Pacific Plate subducts beneath the North American plate.
Define epicentre
The point on the surface of the Earth immediately above the focus of the earthquake.
Following an earthquake, there are two types of body waves (waves within the earth’s interior) occur.
What are S-waves?
What are P-waves?
S-waves are transverse wave travel with a side-side motion, and are able to pass through solids but liquids and gases, since they have no rigidity to support sideways motion.
P-waves travel by compression and expansion, and are able to pass through rocks, gases and liquids.
How does the nature of rock and sediment influence the pattern of shocks and vibrations during an earthquake?
Unconsolidated sediments such as sand shake in a less predictable way than solid rock. Hence the damage is far greater to the foundations of buildings.
How do P-waves influence earthquakes?
P-waves from earthquakes can turn solid sediments into fluids like quicksand by disrupting sub-surface water conditions. This is known as liquefaction and can wreck foundations of large buildings and other waves.
What happens when P and S waves reach the surface?
Some of them can become surface waves. Love waves can cause the earth towards sideways whereas Rayleigh waves cause the earth to move up and down. Surface waves often do the most damage in an earthquake.
What is the main resultant hazards of earthquakes?
How does this hazard have a knock on effect?
The collapse of building structures is the direct cause of many injuries and death, but it also reduces the effect of the emergency services.
