Midterm 2 Flashcards
What is the difference between magma and lava?
Magma is molten material derived from the mantle, but still inside the earth.
Lava is molten material erupted onto the surface of the earth.
What determines explosivity of a volcanic eruption? Be able to explain the roles of silica and dissolved gases and the importance of viscosity and pressure. Explain the relationship between the chemical composition of magma and eruption style and strength?
- Chemical composition of the magma involved in the eruption determines explosivity
- high silica (felsic magma) = high viscosity
- high dissolved gas content in magma = high pressure
- high silica / viscosity and high dissolved gas / pressure = explosive eruptions
· Know the characteristics of Rhyolitic, Andesitic, and Basaltic magma
Rhyolitic: highest silica, highest gas, lowest eruption temp MOST EXPLOSIVE
Andesitic: medium silica, medium gas, medium temperature MEDIUM EXPLOSIVE
Basaltic: lowest silica, lowest gas, highest temperature LEAST EXPLOSIVE
What is the difference between Mafic and Felsic magma?
Felsic magma: lots of silicate chains, a high gas content, erupt at lower temperatures. create explosive eruptions
Mafic magma: low viscosity, lower silica content, lower gas, erupt at higher temperatures. create effusive eruptions.
· What are some of the most common volatiles found in magma? What three key factors determine the viscosity of magma? Why is the viscosity of magma important?
Common volatiles:
water, carbon dioxide
Three key factors determining the viscosity: temperature, silica content, presence of water
Viscosity determines how quickly lava will flow
Explain where volcanos occur, why they occur there, and where we find explosive versus effusive types of volcanos (ie why certain types of eruption are characteristically found in specific tectonic settings).
- Divergent Boundaries: basalts occur here (low explosivity, low silica),
-Intra-plate: ex. Hawaii, basaltic magma (low explosivity)
-Subduction Zone: most violent eruptions because magma is rich in silica and water
- Convergent boundaries: stratovolcanoes, felsic magma with high viscosity but lava flow is not hazardous
Describe the different causes of tsunami formation.
- Earthquakes: earthquakes along reverse or thrust fault subduction zones create tsunamis
- Volcanoes: energy released by volcano along with pyroclastic flow OR volcano eruption can cause a portion of a volcano’s slope to slide off into the ocean
-Landslides: submarine landslide can displace enough water to generate a tsunami
-Asteroid Impacts: asteroid striking ocean creating a tsunami
Be able to explain what distinguishes an active from a dormant volcano
Rest dormant – could erupt again – don’t see anything happen – but smth could
- Extinct – believe magma chambers are not active
Active Volcano:
Recent Eruption: An active volcano has erupted within historical times, typically within the last few thousand years.
Monitoring: Active volcanoes are usually monitored closely for signs of volcanic activity, such as seismic activity, ground deformation, and gas emissions.
Potential Hazard: They pose a potential hazard to nearby populations and infrastructure due to the likelihood of future eruptions.
Dormant Volcano:
A dormant volcano is currently not erupting and has not erupted for a long time, often thousands to millions of years.
Potential for Future Eruptions: While dormant, these volcanoes are not considered extinct and could erupt again in the future under the right conditions.
Monitoring: Dormant volcanoes may not be actively monitored, especially if they are in remote or less populated areas.
What geographical settings typically have the highest levels of fatalities associated with volcanic eruptions and why. Provide specific country examples.
toba – caldera system – indonesia – rhyolitic – high in silica high viscosity – so many volatiles – so much pressure and so much energy released
Yellowstone – caldera
Siberian traps – extreme global temp rise – from gases – temps leathally high - hard to photosynthesize Earths equator – became dead zone
Lahars – columbia Indonesia – pyroclastic flows, tsunamis, tephra, cone collapse
We can forecast eruptions through triangulating data from a number of different forecasting techniques. Briefly describe four forecasting techniques for volcanic eruptions (4 points).
Monitoring – remote sensing, ground deformation, gas emissions monitoring, seismic monitoring
Describe the different types of volcanic hazards, both their causal conditions and the threat they pose to people or property, drawing on real world examples to illustrate your answers. Make reference to the six key characteristics we use to assess physical hazards
- Tephra emissions
- small particles of volcanic rock emitted into the atmosphere
- risk: respiration problems, climate cooling and famine - Gas emissions
-risk: climate cooling and crop failure / famine, potential poisoning - Pyroclastic density current:
- very hot mixture of gases and volcanic tephra that flows down the side of volcano
-risk: destroys everything - Pyroclastic fall
- vertical fall of tephra in the area surrounding an eruption
-risk: thick tephra coverage of areas close to the eruption, collapsed roofs - Lahar
- a flow of mud and debris down volcano
-risk: destruction of anything within the channel - Debris avalanche
- failure of part of volcano
-risk: destruction in path of debris avalanche - Lava flow
-risk: people / infrastructure, but flow is slow
When it comes to natural hazards, the speed at which the hazard occurs often means the difference between property damage or human fatalities. What is the fastest moving volcanic hazard?
pyroclastic flows which can travel up to 200m per second
Define Climate
the weather conditions prevailing in an area in general or over a long period.
What is Albedo?
The percent of energy an object reflects is an object’s albedo
Understand the relationship between solar radiation, earth rotation, and air circulation in order to be able to explain how these give rise to the ITCZ, prevailing winds from the east just north and south of the equator, and the seasonal monsoon rains.
Intertropical Convergence Zone (ITCZ): The convergence of warm, moist air near the equator, combined with the Coriolis effect, results in the formation of the Intertropical Convergence Zone (ITCZ). Here, the trade winds from both hemispheres converge, creating a belt of low pressure. As warm, moist air rises in this region, it cools, condenses, and forms clouds and precipitation.
Prevailing Winds: Near the equator, the Coriolis effect is relatively weak, so the trade winds blow almost directly from east to west. These are known as the northeasterly trade winds in the Northern Hemisphere and the southeasterly trade winds in the Southern Hemisphere. These winds converge at the ITCZ and rise, contributing to the formation of the low-pressure zone.
Seasonal Monsoon Rains: The seasonal shift in the position of the ITCZ is influenced by the tilt of the Earth’s axis as it orbits the Sun, resulting in the changing angle of solar radiation. During the Northern Hemisphere summer, the ITCZ shifts northward, bringing heavy rains to regions like Southeast Asia. Conversely, during the Northern Hemisphere winter, the ITCZ shifts southward, leading to dry conditions in these regions.
Know how topography affects wind and precipitation (orographic lift).
When air must rise over a mountain, the moisture within it cools and condenses to form clouds. One side of the mountain will be moist and cloudy, while the other side remains dry.
What causes low and high pressure at the surface of the earth? How does air move (ie wind) relative to a low and high pressure area at the earths surface? Which way do low and high pressure systems circulate in the a) northern hemisphere and b) southern hemisphere and why?
high pressure systems occur when there is more atmosphere over an area than usual (like from cooling)
low pressure systems are areas when there is atmospheric rising, due to warming and expansion.
air moves from higher to lower pressure
As winds flow from high to low pressure, it is deflected to the right (in the Northern Hemisphere) because of the earth’s rotation. It is in the opposite direction in the Southern Hemisphere. This deflection is nonexistent at the equator and progressively gets stronger towards the poles.
What are the four prerequisite conditions required for the formation of Tropical Cyclones (typhoons/hurricanes
- Very warm surface ocean water through an ocean depth of more than 60 m
- Rotation effection (coriolis) - must be at least 4 degrees of lat away from the equator
- low winder shear (vertical) - significant differences in wind speeds at low and high altitude
- warm and humid air in low (to mid) troposphere, cool air in high troposphere
Be able to graph and describe how wind strength, pressure, and wind direction change as a cyclone moves towards you, is centered on you, and then moves away. Assume we are in the Northern Hemisphere.
Graphical Representation:
Wind Strength Pressure
| /
| /
| /
Strength | /
↑ | /
| | / ← Pressure
| | /
| |/
|\_\_\_\_\_\_\_\_|\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
↑ X-axis (Time/Distance)
↑
↑ Wind Direction (Arrows) Description of Changes: Approaching Cyclone: Wind strength gradually increases. Pressure drops rapidly. Wind direction shifts counterclockwise, becoming more southeasterly.
Cyclone Centered:
Wind strength peaks.
Pressure reaches its lowest point.
Wind direction is variable and may be calm or erratic as the cyclone’s eye passes over.
Cyclone Moving Away:
Wind strength gradually decreases.
Pressure begins to rise.
Wind direction shifts back to its original easterly direction, reversing the counterclockwise pattern observed during the approach.
Globally, where do we find tropical cyclones and why? Why do we not find them off the west coast of South America?
- primarily occur in the tropical regions of the world. They form over warm ocean waters typically between 5 and 30 degrees latitude, both north and south of the equator. The warm ocean waters provide the energy needed for the development and intensification of tropical cyclones
-No tropical cyclones in South America west coast because the presence of cold ocean currents. These cold ocean currents result in cooler sea surface temperatures, which are not conducive to the formation and sustenance of tropical cyclones.
What is the dangerous quadrant of a hurricane? Why is this important? Be able to identify the dangerous quadrant of a tropical cyclone in both the northern and southern hemisphere and relative to the direction of travel of the storm. If you could only move perpendicular to the storm direction, know which way you would have to go to avoid the dangerous quadrant.
- right front quadrant of a hurricane is most dangerous (south front in S. Hemisphere)
-This quadrant is considered the most dangerous because it typically experiences the strongest winds, highest storm surge, and heaviest rainfall associated with the storm.
-It’s important to identify the dangerous quadrant of a tropical cyclone because it helps determine the areas most at risk for severe impacts such as destructive winds, storm surge, and heavy rainfall. - to avoid you would need to move east in both scenarios (right in NH and left in SH)
What are the hazards associated with hurricanes? How do they differ at sea and over land?
- High wind
- Store surge (over coastal areas) or waves (at sea)
- Precipitation (flooding and mass movements)
- Thunderstorms and Tornadoes
What are the causes of storm surge? Where is storm surge the greatest?
What is a Rogue wave and what causes them?
What causes heat waves?
High pressure ridge traps warm moist layers next to ground
How are temperature and mean average mortality related?
Temperature and mean average mortality are positively correlated – more ppl die on extremely hot days – spike in mortality during heat waves – mostly affecting older/vulnerable ppl
Why is humidity important in assessing hazard to humans from heat waves?
- it affects the body’s ability to cool itself through the process of sweating and evaporation. When humidity levels are high, sweat evaporates more slowly, which diminishes the body’s natural cooling mechanism.
How is apparent temperature calculated?
Air temperature + (relative) humidity lvl (%)
Wind chill – temp + wind
Why are urban populations more exposed and vulnerable to heat waves?
Because the apparent temperatures are higher, heat is trapped in by buildings and people
