Volcanic Hazards The problems with humans and volcanoes
Volcanic Hazards The problems with humans and volcanoes existing in adjacent spaces
Your list of volcanic hazards • Ash falls • Stagnant gases suffocate animals • Lava flow into seaport • Air pollution with sulfur • Crops destroyed • Turns day to night • Acid in lakes destroys the fish • Lava blocks roads • Homes are destroyed • Farms flooded with lava • People die
Let’s see what the experts say.
Background Information • Many kinds of volcanic activity can endanger the lives of people and property both close to and far away from a volcano. • Most hazards involve the explosive ejection or flowage of rock fragments and molten rock in various combinations of hot or cold, wet or dry, and fast or slow.
Background Information cont. • Volcanic explosions can drastically alter land water for tens of kilometers around a volcano. • Ash and sulfuric acid erupt into the stratosphere and can change our planet’s climate temporarily. • People often have to evacuate their homes for days and sometimes forever.
Background Information cont. • Buildings, crops, industrial plants, transportation systems, and electrical grids can be damaged by tephra, lahars, and flooding. • Since 1700 AD volcanoes have killed more than 260, 000 people, destroyed entire cities, blown down forests, and severely disrupted local economies for months, even years.
Who is at risk? • The population at risk from volcanoes is 500 million (one-half billion) • Therefore, prediction and warning of eruptions is important. • Planning to prevent people living in the highest risk zones is also important.
Major Types of Hazards • Tephra • Lahars • Pyroclastic flows • Lava flows • Landslides • Gas
Tephra • General term for fragments of volcanic rock and lava that are blasted into the air by explosions or carried upward by hot air.
Types of Tephra • Determined by size – Ash: < 2 mm (less than 2 millimeters) – Lapilli is 2 - 64 mm – Blocks > 64 mm ejected while solid – Bombs > 64 mm ejected while molten
Tephra Dangers • The danger of blocks and bombs falling out of the sky is obvious. • Let’s look at other less crashingly obvious hazards.
Dangers of Tephra • Ash can travel thousands of kilometers. • Ash can circle the globe. • Ash can block out sunlight. (Remember, 1860 the year without summer which led to crop failure and starvation of 80, 000. ) • Ash can change the weather. • Ash mixed with water are debris flows.
Ash disrupts economies • Ash covers crops. • Ash clogs waste water systems. • Ash may shut down power systems (Ash is highly conductive when wet, causing electrical shorts). • Ash abrades paint.
Ash and safety • Ash with water makes roads slippery. • Ash stalls jet engines and those of trucks and cars. • Roofs may collapse from added weight. • Ash causes electrical fires.
If that was not scary enough, let’s look at an even greater danger. . .
Pyroclastic Flows
Pyroclastic Flows cont. • A pyroclastic flow is a groundhugging avalanche of hot ash, pumice, rock fragments, and volcanic gas that rushes down the side of a volcano as fast as 100 km/hour or more.
Pyroclastic Flows cont. • The temperature within a pyroclastic flow may be greater than 500° C, sufficient to burn and carbonize wood!
What do you think? • What are the dangers of pyroclastic flows? • Could you out run a pyroclastic flow?
Landslides • Landslides are large masses of rock and soil that fall, slide, or flow very rapidly under the force of gravity.
Landslides • Landslides are large masses of rock and soil that fall, slide, or flow very rapidly under the force of gravity. • Leaves a horse-shoe shaped crater.
Landslides cont. • The high velocity (>100 km/hr) and great momentum of landslides allows them to run up slopes and to cross valley divides up to several hundred meters high. • Landslides can dam rivers.
Mt. St. Helens Landslide • For example, the landslide at Mount St. Helens on May 18, 1980, had a volume of 2. 5 km 3, reached speeds of 50 -80 m/s (180288 km/hr), and surged up and over a 400 m tall ridge located about 5 km from the volcano!
Results of landslides • Destroys everything in its path
What do you think? What are the economic effects of a landslide?
Lahars
Lahars • Lahar is an Indonesian term that describes a hot or cold mixture of water and rock fragments flowing down the slopes of a volcano and (or) river valleys. • When moving, a lahar looks like a mass of wet concrete that carries rock debris ranging in size from clay to boulders more than 10 m in diameter.
What causes Lahars? • Volcanoes melt snow and glaciers causing Lahars. • The eruption of Mt. St. Helens caused Lahars.
Armero Lahar • Within four hours of the beginning of the eruption, lahars had traveled 100 km • Left behind a wake of destruction: more than 23, 000 people killed, about 5, 000 injured, and more than 5, 000 homes destroyed
Lava Flows
Lava Flows • Lava flows are streams of molten rock that pour or ooze from an erupting vent. • Lava is erupted during either nonexplosive activity or explosive lava fountains.
Lava moves slowly • Lava flows destroy everything in their path. • But most move slowly enough that people can move out of the way. • But they typically advance less than 1 km/hour on gentle slopes.
Lava Destroys • Everything in the path of an advancing lava flow will be knocked over, surrounded, or buried by lava, or ignited by the extremely hot temperature of lava.
Lava is Permanent • People can recover from other disasters – Hurricanes – Floods • People can rebuild – Homes and communities • When lava covers your home or farm digging out is not possible.
Lava + Glaciers = Lahars • When lava erupts beneath a glacier or flows over snow and ice, melt water from the ice and snow can result in farreaching lahars.
Gas
Volcanic Gases • Are the driving force of eruptions. • And they are dangerous. • The dangerous gases are: – Sulfur dioxide – Carbon dioxide – Hydrogen fluoride
Dangerous gases • Sulfur dioxide – Leads to acid rain locally and pollution downwind. – Volcanologists wear respirators to protect their lungs from the burning fumes. – In stratosphere sulfur aerosols leads to lower surface temperature and promotes depletion of the ozone layer. • Carbon dioxide – Is heavier than air – It flows into low lying areas and collects in the soil. – It is lethal to plants, animals, and humans. • Hydrogen fluoride – Deform or kill animals that graze on vegetation coated with volcanic ash with fluorine-compounds.
C 02 Death of Trees
Volcanic Smog
Now let’s read about Mt. Rainier.
References • USGS Volcano Hazards Program http: //volcanoes. usgs. gov/Hazards/What/haz ards. html • http: //volcanoes. usgs. gov/Imgs/Jpg/Mayon/ 32923351 -020_caption. html
The End
Effects of Earthquakes • • • Sounds Cracks Landslides Destruction By Fire Tsunami Loss of Life
Loss of Life • People are able to check out in many different ways during an earthquake… most die from man-made structures collapsing on them… • From earliest recorded history over 16 million folks have checked out due to earthquake activity
Tsunami • Caused by rapid movement of the ocean floor… these waves appear as a simple rise in sea level and are noticed by ships at sea… they only become visible when they pile up as the wave comes ashore… as the wave bunches up, the water recedes for miles to come crashing back… • Illustrate tsunami formation
Destruction by Fire • Gas mains are ruptured by breakage and fires result… water mains are also ruptured so the fires can’t be fought… • only 5% of the devastation of the 1906 San Francisco quake was caused by the actual shaking… the rest (which leveled countless city blocks) was from fire
Causes of Landslides • intrusion of magma into a volcano • explosive eruptions (magmatic or phreatic--steamdriven explosions) • large earthquake directly beneath a volcano or nearby (typically >M 5) • intense rainfall that saturates a volcano or adjacent tephra-covered hillslopes with water, especially before or during a large earthquake
Carbon dioxide • Colorless and tasteless, but deadly – 5% increase in respiration. – 10% causes shortness of breath, headaches, dizziness, sweating, and restlessness. – 15%causes impaired coordination & muscle contraction. – 20% causes loss of consciousness and convulsions. (>20% causes death. )
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