Humans are at the mercy of natural
hazards. Predicting hazards and surviving them has always been vitally
important. Australian Aboriginal stories of volcanic eruptions are, arguably,
the oldest records of natural disasters and have been faithfully repeated for
thousands of years. These stories not only describe the volcanic eruption, but
also warn people to evacuate the area when warning signs are detected.
More recently, people have developed
technologies to record and locate hazards. An example of this is the beautiful
seismograph invented by Chinese astronomer Zhang Heng. However, prediction of
hazards is difficult and varies with the type of event.
A replica
of the instrument invented by astronomer Zhang Heng to warn the Chinese Emperor
of earthquakes. Ground movement moves a pendulum inside the jug, pushing a
lever that opens a dragon’s mouth. A ball drops out into the mouth of the toad.
This indicates not only that an earthquake has occurred, but also the direction
of the hazard. (Kowloonese 2004, Wikimedia Creative Commons)
Webpages:
- Is an Aboriginal tale of an ancient volcano the oldest
story ever told?
- (Science)
- When the bullin shrieked: Aboriginal memories of volcanic eruptions thousands of years ago
- (The Conversation)
Modern technologies to predict
natural disasters
One of the best predictors of
geological and weather hazards is historical records. If a disaster has
happened in the past, it is likely to occur again. Understanding the risk
allows people to minimise damage to lives and property.
Geohazards
Modern seismographs are not
as beautiful as that of Zhang Heng, but they are far more compact and accurate.
Different patterns and magnitudes of seismic activity provide information about
the movement of magma under volcanoes and the spread of seismic waves in
earthquakes. Networks of seismometers are vital for predicting volcanic
eruptions and recording earthquakes.
Strain meters measure tiny differences in forces
affecting Earth’s crust. They can detect movement of magma and strain along
fault lines. Strain meters are so sensitive that they can detect changes caused
by passing weather fronts!
GPS is useful for monitoring movement along plate
and fault boundaries, as well as detecting changes in the shape of a volcano.
If GPS monuments are moving closer together, this indicates compression of
Earth’s crust. This stored energy could eventually be released in an
earthquake. The movement of magma within a volcano can cause swelling which is
detected by increased elevation and spreading of GPS monuments.
Gas monitoring is important for prediction of
volcanic eruptions. Increases in carbon dioxide and sulfur dioxide indicate the
movement of magma and imminent eruptions. Gases can be directly sampled or
measured using spectrometers either on the ground or in aircraft. Monitoring of
radon gas for earthquake warnings has been proposed but does not offer accurate
predictions at this time.
Different types of radar (InSAR
and LiDAR) allow scientists to monitor the shape of volcanoes. The resulting
images can be used to highlight changes in shape and even to monitor ash
emissions.
Weather hazards
Air pressure is a key monitoring technique used
to forecast extreme weather events. The interaction of high- and low-pressure
systems can create violent storms such as East Coast Lows and tropical
cyclones. Pressure is monitored using barometers on land and on ocean vessels.
Temperature
of both air and oceans is also important in predicting weather patterns. Sea
surface warming is associated with longer term weather patterns such as El Niño
and smaller patterns such as tropical cyclones and East Coast lows. Temperature
is monitored using thermometers on land and at sea, as well as satellite images.
Doppler
radar detects precipitation. It is useful for mapping the progress and
intensity of rain and may offer very short-term warning about extreme hail.
However, it is not useful for prediction of major hazards.
Sea surface temperature map created using the Moderate
Resolution Imaging Spectroradiometer on NASA’s Aqua satellite. Warmer
temperatures are pink yellow. Grey indicates landmasses or sea ice. (NASA,
public domain from https://earthobservatory.nasa.gov/global-maps/MYD28M)
Webpages:
- Comprehensive monitoring provides timely warnings of volcano reawakening(USGS)
- Earthquake Hazards: Monitoring(USGS)
- Learn about forecasts from the Bureau of Meteorology(BOM)
Protecting people and property
The purpose of hazard prediction is
to prevent or minimise damage to people and property. Without disaster
planning, prediction is useless and may cause damaging panic. If a warning is
issued, people must know how to respond. The Columbian government was warned of
the eruption of Nevado del Ruiz volcano in 1983, but no warning was given to
the population. The resulting lahars killed more than 23,000 people.
Building codes are vital to prevent loss of life.
Earthquake zones need buildings that are reinforced to withstand earth
movement. Reinforced structures are also more likely to withstand extreme
weather events. Steeply pitched, reinforced roofs are most likely to hold up
under ash fall from a volcanic eruption. Placing homes away from areas of
potential storm surge, landslide or lahar hazards is just as important as
reinforcement of the structure itself.
Disaster planning needs to be undertaken by
governments so they can effectively respond to natural hazards through
evacuations and prompt restoration of disrupted gas, water and electricity.
Emergency services and ordinary citizens must know how to react if a hazard
strikes. Japan is a world leader in disaster response and holds an annual
Disaster Prevention Day on September 1. Citizens learn how to respond in school
and at the workplace.
Model of
two buildings with (right) and without (left) base isolation for earthquake
resistance. Chicago’s Field Museum. (Shustov 2008, Wikipedia Creative Commons)
Webpages:
- Disasters and disaster prevention in Japan(Ministry of Foreign Affairs of Japan)