Natural Hazards

Threats to large cities Naturally occurring dangers Man-made dangers

Naturally occurring dangers  Cities are located in regions (areas) that make them vulnerable to naturally occurring dangers.  Some people settle near the sea, in regions that are prone to floods, hurricanes or tsunamis.

Some cities are built at the base of volcanoes and live under constant threat of volcanic eruptions.

Man-made dangers  This type of danger is linked to human activity Examples: a)Factories use dangerous chemicals b)Nuclear power plant explosion (meltdown) c)War (nuclear bomb)

What is a natural phenomenon? It is basically a naturally occurring event that is observable (Ex: watching a volcanic eruption)

What is a natural hazard? natural disaster?  Natural hazards are severe and extreme weather and climate events (something that happens) that occur naturally  Some regions are more vulnerable to certain hazards than others.

 Natural hazards become natural disasters when people's lives, property, businesses, roads, etc. are destroyed

Types of Disasters Disasters can take many different forms, and the duration can range from an hourly disruption to days or weeks of ongoing destruction. Below is a list of the various types of disasters – both natural and man-made or technological in nature – that can impact a community.

Natural Types of Disasters Damaging Winds Drought and water shortage Earthquakes Emergency diseases (pandemic influenza) Extreme heat Floods and flash floods overview/types-of-disasters/

Hail Hurricanes and tropical storms Landslides & debris flow Thunderstorms and lighting, tornadoes, tsunamis Wildfire Winter Ice storms Sinkholes

What is a Tornado? It is a narrow, violently rotating column of air. Because wind is invisible, it is hard to see a tornado unless it forms a condensation funnel made up of water droplets, dust and debris. l-LtD7LN0w

What is an earthquake? They are sudden rolling or shaking events caused by movement under the earth’s surface. They happen along cracks in the earth's surface, called fault lines, and can be felt over large areas, although they usually last less than one minute.

What is a flooding? Flooding is an overflowing of water onto dry land. It can happen during heavy rains, when ocean waves come on shore, when snow melts too fast, or when dams or levees break. omJIw

Volcanic Eruptions  It occurs when molten rock, ash and steam pour through a vent in the earth's crust.  Volcanoes are described as active (in eruption), dormant (not erupting at the present time), or extinct (having ceased eruption; no longer active).  Some volcanoes explode. Others are slow- flowing fountains of lava, which is hot fluid rock.

Famous volcanic eruption:  Where: Italy  When: A.D. 79  The eruption of Mount Vesuvius buried the towns of Pompeii and Herculaneum under 20 feet of ash and lava, killing an estimated 20,000 people.  The ash that buried the town and the people also preserved them.  The work of uncovering the ancient cities began in 1748 and continues to this day.

What is a Plinian eruption?  Plinian eruptions, also known as Vesuvian eruptions, are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79. The eruption was described in a letter written by Pliny the Younger; it killed his uncle, Pliny the Elder.volcanic eruptionseruption of Mount Vesuvius in AD 79Pliny the YoungerPliny the Elder  Plinian eruptions are marked by columns of gas and volcanic ash extending high into the stratosphere, the second layer of Earth's atmosphere. The key characteristics are ejection of large amount of pumice and very powerful continuous gas blast eruptions.gasvolcanic ashstratospherepumice  Short eruptions can end in less than a day, but longer events can take several days to months. The longer eruptions begin with production of clouds of volcanic ash, sometimes with pyroclastic flows. The amount of magma erupted can be so large that the top of the volcano may collapse, resulting in a caldera. Fine ash can deposit over large areas. Plinian eruptions are often accompanied by loud noises, such as those generated by Krakatoa.cloudspyroclastic flowsmagmacalderaKrakatoa

The city of Pompeii was an ancient Roman town-city near modern Naples in the Italian region of Campania, in the territory of the comune of Pompei. Pompeii, along with Herculaneum and many villas in the surrounding area, was mostly destroyed and buried under 4 to 6 m (13 to 20 ft) of ash and pumice in the eruption of Mount Vesuvius in 79 AD. Kg0Bc

WHEN is a city “subject to hazard”?  A phenomenon is considered hazardous when lives are at risk.  Examples of events that can threaten our lives: a)An earthquake b)An epidemic (contagious virus!) c)An explosion at a nuclear plant

Characteristics of a hazardous event:  Death  Property damage to homes, neighborhoods etc.  Economic losses because jobs are affected when companies are destroyed.  Environmental damage caused by the natural disaster (ex: wild fires)

Are there risk-free territories?  No!  Some cities are more at risk than others and may be threatened by more than one natural hazard.

CASE STUDY: San Francisco, California

San Francisco It is a large city located in California, on the west coast of the United States. The San Francisco metropolitan area, however, has a population of more than 7.4 million.

Demographics of San Francisco It is a multiethnic city and holds many parades to celebrate its cultural diversity.

San Francisco’s economy It is famous for Silicon Valley. Silicon Valley has played a huge growth in San Francisco’s economic growth.

The name silicon valley refers to the silicon that’s used to make integrated circuits and chips in bank cards/smart cards. This region is home to information technology and electronic giants like Apple, Google and Facebook.

San Francisco is under threat San Francisco is at risk because it was built next to the San Andreas Fault. This geological fault is part of a group of faults located at the meeting point of two major tectonic plates: Pacific Plate and North American Plate. =ZxPTLmg0ZCw

Predicting earthquakes to prevent devastation Historical earthquakes in San Francisco: hit by an earthquake (7.9 on the Richter scale) and was accompanies by fires caused by broken gas lines. Large section of city destroyed 1957 and 1989 – killed 63 people and injured another It also caused a section of the highway to collapse.

Installation of seismic wave sensors A network of seismic wave sensors have been installed throughout the metropolitan region to predict earthquakes. Recordings are analyzed by seismologists. This information is used to create a map of the areas that are most in danger.

Hard rocks vs. Loose, soft soil The shocks that occur underground during an earthquake are transmitted differently depending on the type of soil they travel through. a)Hard rock: does not transmit seismic waves very well therefore little damage is done to structures about it. b)Loose, soft soil: Soil that is made of sand, mud or gravel run a higher risk of damage.

Introduction of strict construction guidelines All new buildings must meet the strict construction guidelines for the following: a)Foundations b)Doors and windows c)Construction sites Older buildings, that were built before these guidelines came into existence, are in danger because they can be more damaged by earthquakes.

Consequences of a natural disaster The ability to recover from a natural disaster and the severity of consequences that disaster depends on country’s level of development. Countries around the world are labelled developed or developing.

Natural disasters in Developed countries Developed countries are wealthy. The health system comes to the aid of victims quickly. Emergency services respond to the public’s needs. Most victims are covered by an insurance policy that will help them pay for damages (ex: new place to live, new furniture and appliances, etc.).

Natural disasters in Developing countries Developed countries are poor. The health system is inadequate and almost non- existent during a disaster. Emergency services are inadequate and non-existent too. Few people can afford insurance (no payment for damages, end up homeless, etc.). Government does not have the financial means (money) to help victims.

International aid International and humanitarian organizations arrive on the scene to offer first aid and temporary shelter, and organize help. These organizations also distribute food and water, and make sure that medical care is available. Money is also need to remove the rubble and debris and rebuild homes.

Why do we continue living in big cities subject to natural disasters?  Good economy (well-paying jobs)  We are attached to places, friends, family.  We do not have the means (money) to move to another region.  All territories involve some degree of risk.

Inequality in the face of natural hazards  Industrialized (wealthy) countries are well-equipped to deal with natural disasters.  These countries also have the money, equipment and the necessary resources to rebuild.  Its citizens also receive food, shelter and medical care from government organizations  This is not the case for developing (poor) countries.