Hazardous Environments Flashcards
(32 cards)
Definition of a hazard
A physical event that may potentially cause damage to people
Definition of risk
Exposure of people to a hazardous event
Disaster
The realisation of risk
Vulnerability
The susceptibility to loss
Describe and explain a divergent plate boundary and the hazards associated (draw diagram)
DIAGRAM draw correctly
- shallow, weak and narrow belt of earthquakes due to weak volcanic activity (basaltic lava, low silica content)
=> harmless at oceanic boundary
- little risk to humans
Describe and explain a conservative plate boundary and the hazard associated
DIAGRAM
- shallow and powerful earthquakes
- relatively narrow belt
=> hazardous to human life because human settlements may be in close proximity + they are powerful
Describe and explain a destructive convergent plate boundary and associated hazards
DIAGRAM
- deepest and most powerful earthquake
- broader belt of earthquakes
- highly explosive volcanoes(andesitic volcanic eruptions)
=> although there are mountains which may reduce population density, associated risk of landslides and there are likely to be human settlements on the coast
Describe and explain a collision plate boundary and associated hazards
DIAGRAM
- shallow, broad zones of seismic activity
Types of waves
Body waves: P-waves (fastest and longitudinal) & S-waves (slowest and transverse)
Surface waves: Love waves and Raleigh waves
Two seismic scales
Modified Mercalli scale: subjective & qualitative, measure of intensity
Moment Magnitude scale: calibrated measure of energy release, logarithmic scale
Three secondary hazards earthquakes + brief explanation
- Soil liquefaction - loose sand and silt that is saturated with water can behave like a liquid when shaken by an earthquake. Pore water pressure increases so sand grains lose contact with each other. Soil loses its ability to support structures.
- Mass movements - may be triggered by earthquakes, reducing the shear strength of the slope for a short time period
- Tsunami - when a large volume of water is instantaneously displaced vertically du to upward or downward movement of the sea bed -> becomes especially hazardous once in increases in height as it approaches the shore with a shallowing sea bed
6 types of volcanoes with brief description
- Fissure volcano - gentle basaltic slope
- Shield volcano - gentle slope of basaltic lava flows
- Dome volcano - steep convex slope from thick and fast-cooling lava
- Ash-cinder volcano - cinder, fine ash
- Composite volcano - branch pipe (stratovolcano)
- Caldera volcano - old cone, new cone -> highly explosive
7 types of volcanic eruption
- Pelean eruption - highly viscous magma -> explosion out of weakness in the side of volcano
- Plinian eruption - very violent explosion resulting in narrower cloud e.g. Mt Pinatubo
- Icelandic eruption - fluid basalts issue quietly from fissures and mid-oceanic ridges
- Hawaiian eruption - fluid basalts issue from vents in volcanoes. Gases escape easily and quietly with occasional spurts of gases form lava lakes causing lava fountains.
- Strombolian eruption - less fluid lava and gases escape with moderate explosions in which lava bombs are ejected
- Vulcanian eruption - eruptions more violent as more viscous lava solidifies more quickly and traps gases. Tephra released + ash-laden clouds in mushroom shape
- Vesuvian - high gas content, long periods of inactivity, wide and dark ash cloud
Nuees ardentes
Dark glowing, fast-moving, incandescent mass of gas - enveloped particles that is associated with certain types of volcanic eruptions (contain dense lava fragments derived from a growing lava dome) e.g. Martinique 1902
Lava flows
Streams of molten rock that poor or ooze from an erupting vent. with speed depending on the… type of lava, viscosity, steepness, width of flow, rate of lava production
Lahar
A hot or cold mixture of water and rock fragments that flows down the slopes of a volcano
Pyroclastic flows
80/100 km/hr, between 200-700 degrees celcius
Contains a high density mix of hot lava blocks, pumice, ash and volcanic gas
Ash fallout and tephra
Fragments of rock that are produced when magma or rock is explosively ejected;
ashes < 4mm, cinders 4-5mm, lapilli are pebble sized, volcanic block are large fragments
Steam and poisonous gas emission
Magma contains dissolved gases which provide the driving force that causes most volcanic eruptions - Mt Pinatubo released 250 megatons of gas
Characteristics of basaltic lava
Low viscosity, hotter (up to 1200 degrees), lower silica content, associated with frequent but gentle eruptions, found at constructive margins and hotspots
Andesitic
High viscosity, less hot (900 degrees), higher silica content, pyroclastic flows likely, destructive margins, infrequent but violent eruptions
Aa lava
Free chunks, lava flows rapidly, viscosity increases as heat is lost quickly, up to 10m thick
Pahoehoe lava
Smooth surface, slow flow, flows far
Factors contributing to increased sheer stress
Undercutting/slope steepening (erosion)
Loading of slope - weight of water, infrastructure etc.
Lateral pressure - water in cracks, subsequent freezing
Transient stress - earthquakes or winds
