Download Geologic Hazards

Geological Hazards
or…
When Mother Earth is a Bitch
Geological Hazards
• The most dangerous geologic hazards are
earthquakes, volcanic eruptions, landslides, floods,
and tsunamis
• Geologists strive to understand Earth processes to
alert, warn, and possibly predict dangerous geological
events
Geological Hazards
• Earthquakes
– Sudden release of energy; shaking can damage
buildings and break utility lines (electric, gas, water,
sewer)
– Much of the urban damage during an earthquake is
caused by fires from broken utility lines
Geological Hazards
• Volcanoes
– Falling volcanic debris, lava flows, and magmatic
earthquakes cause some damage
– Pyroclastic flows and mudflows, however, are the
most dangerous to human civilizations
Geological Hazards
• Landslides, Floods, and Tsunamis
–(we’ll cover these on another day…)
• Compositional Layers of Earth
- Crust
• Very thin outer rocky shell of Earth
- Mantle
• Hot solid layer that sometimes moves
slowly over time
- Core
- The densest layer of the Earth, at the
center, metallic
• Near surface zone
– Lithosphere (~100 km thick)
• Solid, strong, rigid/brittle outer shell of Earth
• Composed of both crust and uppermost mantle
• Makes up Earth’s tectonic “plates”
– Asthenosphere (extends downward ~100-350 km)
• Heat-softened yet solid rock
• Plastic (capable of flow) zone on which the
lithosphere “floats”
Theory of Plate Tectonics
• Continental Drift Hypothesis (Alfred Wagner)
– Theory which explains the “fit of continents”,
common rocks and fossils across ocean basins
• Plate Tectonics Theory
– Describes lithosphere as being broken into plates
that are in motion
– Explains origin and locations of such things as
volcanoes, fault zones and mountain belts
Tectonic Plate Boundaries
There are three types of plate boundaries
1) Divergent / Spreading – plates move apart, usually at midocean ridges, produces new land
2) Convergent / Subduction - plates move toward each other,
usually forms mountains and volcanoes
3) Transform - plates slide past one another, causes fault zones
and earthquakes (i.e., San Andreas fault in California)
VOLCANOES
• Volcanoes – cone-shaped or domeshaped landform created by emission of
lava and gases from a constricted opening
• Magma rises through a narrow pipelike
conduit – a volcanic neck
WHY DO MAGMAS RISE AND
ERUPT ?
• BUOYANCY – hot magma is less dense
than overlying rocks
• HYDROSTATIC PRESSURE – Buoyancy
of magma below puts pressure on entire
column of magma forcing it upwards
VOLCANIC SHAPES
• Three basic shapes due to magma and
eruptive style
– Composite Volcanoes
– Shield Volcanoes
– Cinder Cones
Composite Volcanoes
Composite Volcanoes are
very tall, 1000s of feet.
Most tend to have snow,
ice and even glaciers at top
SHIELD VOLCANO IMAGES
• Fluid, basaltic lava
erupts onto the
surface and flows
freely across the
ground for great
distances forming a
broad cone.
CINDER CONE VOLCANOES
• A cinder cone is a steep, conical hill of
volcanic fragments that accumulate
around and downwind from a vent
PYROCLASTIC FLOWS
PYROCLASTIC FLOWS
• A ground-hugging 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.
• The temperature within a pyroclastic flow
may be greater than 500° C, sufficient to
burn and carbonize wood.