Earthquakes, Volcanos, Tsunamis
Earthquakes
Definition: Earthquakes are seismic events caused by the movement of tectonic plates on the Earth's crust.
Cause: The movement is driven by the asthenosphere, a fluid layer beneath the crust, which builds up pressure between tectonic plates that eventually causes them to slip, resulting in an earthquake.
Transform Faults:
Example: San Andreas Fault in California.
Characteristics:
The Pacific Plate is moving north, while the North American Plate is moving south.
As these plates rub against each other sideways, stress accumulates until released as an earthquake.
Major Earthquakes:
Largest recent earthquake: San Francisco Earthquake (1906)
Significant destruction due to buildings made from brick, which crumble under seismic activity.
Current expectations suggest a major earthquake is overdue along the fault due to accumulated pressure, likely starting from the Salton Sea.
Preparedness:
Importance of having provisions (water, food) ready due to the potential for infrastructure collapse (bridges, freeways).
US Geological Survey (USGS):
Monitors seismic activity worldwide, providing real-time data on recent earthquakes, mapping fault lines, and energy release.
Measurement Scale:
Richter Scale: Measures earthquake magnitude on a logarithmic scale from 0 to 10.
Key points on the scale:
An increase of 1 unit on the Richter scale represents 10 times more shaking and 33 times more energy release.
Generally, feelable earthquakes start at around , with severe damage expected for those and above.
Tsunamis
Definition: Tsunamis are large ocean waves caused primarily by underwater seismic activity (earthquakes).
Mechanism:
Typically triggered at convergent fault lines where one tectonic plate is pushed down while the other is pushed up.
This movement displaces a large volume of water, creating a wave that travels towards shore.
Wave Behavior:
In the open ocean, tsunami waves are not very tall but gain height as they approach land due to shallower water.
Warning sign of an impending tsunami: water retracting (sucking back) before the wave hits.
Characteristics:
Tsunami waves can be extremely destructive, often leading to multiple waves following the initial impact.
Case Study:
2011 Japan Tsunami:
Triggered by a earthquake, the tsunami waves reached heights of 40 meters (approximately 133 feet), devastating coastal areas and causing over 15,000 deaths. Also triggered the Fukushima nuclear power plant meltdown.
Volcanoes
Definition: Volcanoes are geological formations that occur when magma from beneath the Earth's crust escapes to the surface.
Formation Mechanism:
Commonly associated with convergent plate boundaries where tectonic plates converge.
One plate dives beneath another, creating a subduction zone that produces magma due to melting crust, leading to volcanic eruptions.
Effects of Eruptions:
Eruptions can discharge solid materials, volcanic gases (potentially toxic), and ash that impact air quality and, in severe cases, local climate due to atmospheric particle dispersion.
Hot Spots:
Areas of volcanic activity that occur in the middle of tectonic plates, such as in Hawaii, due to heat from the mantle rather than being at a plate boundary.
Over time, as tectonic plates drift over a fixed hot spot, new volcanic islands are formed, leading to chains of islands with older volcanoes furthest from the hot spot.
Hawaiian Islands Example:
The oldest volcanic islands (about 5 million years old) are farthest from the hot spot, while newer islands (a few million years old) are closer to the active region.
Active volcanism continues to expand the region as new lava seeps out.
Volcanic Effects Overview:
Volcanic eruptions can lead to explosive outbursts, air quality issues, and influence climate by blocking sunlight with ash particles.