Database results:
    examBoard: Cambridge
    examType: IGCSE
    lessonTitle: Storm Surges and Tsunamis
Environmental Management - Managing Natural Hazards - Flooding - Storm Surges and Tsunamis - BrainyLemons
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Flooding » Storm Surges and Tsunamis

What you'll learn this session

Study time: 30 minutes

  • The difference between storm surges and tsunamis
  • Causes and formation of storm surges and tsunamis
  • Environmental and human impacts of these coastal flooding events
  • Case studies of significant storm surge and tsunami events
  • Management strategies and early warning systems
  • How to prepare for and respond to these hazards

Understanding Storm Surges and Tsunamis

Storm surges and tsunamis are two powerful coastal flooding events that can cause devastating impacts on coastal communities. While both involve large volumes of water moving inland, they have different causes, characteristics and warning times.

Key Definitions:

  • Storm Surge: An abnormal rise in sea level during a storm, measured as the height of water above the normal predicted astronomical tide.
  • Tsunami: A series of ocean waves with very long wavelengths (up to 200km) caused by large-scale disturbances of the ocean, typically from earthquakes, volcanic eruptions, or underwater landslides.

🌊 Storm Surges

Storm surges are caused by wind and atmospheric pressure changes from tropical cyclones, hurricanes, or severe storms. As strong winds push water toward the shore, it builds up and creates a dome of water that can be 2-9 metres higher than the normal tide level. Low atmospheric pressure also contributes by allowing the water surface to rise higher than normal.

🌊 Tsunamis

Tsunamis are typically triggered by underwater earthquakes, volcanic eruptions, or landslides. When the seafloor suddenly moves vertically, it displaces the water above it, creating waves that travel outward in all directions. Unlike normal waves, tsunami waves involve the movement of water all the way to the ocean floor, giving them enormous energy and destructive power.

Formation and Characteristics

Storm Surge Formation

Storm surges develop when several factors combine:

  • Wind force: Strong winds push water toward the shore
  • Low pressure: The low atmospheric pressure in a storm allows the water level to rise
  • Shallow coastal waters: Water piles up more easily in shallow areas
  • Coastal shape: Bays and estuaries can funnel and amplify the surge
  • Timing with tides: A surge arriving during high tide creates even higher water levels

Storm surges typically last for several hours and affect coastlines over tens to hundreds of kilometres. They provide limited warning time, usually hours to days, depending on storm tracking capabilities.

Tsunami Formation

Tsunamis form through a three-stage process:

  1. Generation: Sudden displacement of water, usually from seafloor movement during an earthquake
  2. Propagation: Waves travel across the open ocean at speeds of 500-800 km/h
  3. Inundation: As waves approach the shore and enter shallow water, they slow down but grow dramatically in height

In deep ocean, tsunami waves may be only 30-60 cm high but can be hundreds of kilometres long. When they reach shallow water, they can grow to heights of 10-30 metres. Warning times vary from minutes (for local tsunamis) to several hours (for distant tsunamis).

🚩 Warning Signs

For tsunamis: Rapid sea level retreat exposing the seafloor, unusual roaring sounds from the ocean, earthquake shaking in coastal areas. For storm surges: Weather forecasts, hurricane/cyclone warnings and gradually rising water levels.

📊 Measurement

Storm surges are measured using tide gauges and storm surge models. Tsunamis are detected by DART (Deep-ocean Assessment and Reporting of Tsunamis) buoys, tide gauges and seismic monitoring systems.

📅 Frequency

Major storm surges occur several times annually worldwide, typically during hurricane/cyclone seasons. Major tsunamis are less frequent, with devastating events occurring roughly once per decade globally.

Environmental and Human Impacts

Immediate Impacts

Both storm surges and tsunamis can cause:

  • Loss of human life and injuries
  • Destruction of buildings, infrastructure and property
  • Contamination of freshwater supplies with saltwater
  • Erosion of beaches and coastal landforms
  • Damage to natural habitats like mangroves, coral reefs and coastal wetlands

Long-term Impacts

The aftermath of these events can lead to:

  • Soil salinisation affecting agriculture for years
  • Economic losses from damaged industries and infrastructure
  • Displacement of coastal communities
  • Psychological trauma and health issues
  • Changes to coastal ecosystems and biodiversity

Case Study: 2004 Indian Ocean Tsunami

On 26 December 2004, a massive undersea earthquake (magnitude 9.1) off the coast of Sumatra, Indonesia, triggered one of the deadliest tsunamis in recorded history. The tsunami waves reached heights of 30 metres in some areas and affected 14 countries across Asia and Africa. Over 230,000 people were killed, with Indonesia, Sri Lanka, India and Thailand suffering the greatest losses. The tsunami caused approximately £7.5 billion in damage and left millions homeless. This disaster highlighted the lack of tsunami warning systems in the Indian Ocean and led to the development of the Indian Ocean Tsunami Warning System.

Case Study: Hurricane Katrina Storm Surge (2005)

Hurricane Katrina produced a storm surge of 8-9 metres along parts of the Mississippi coast and 3-6 metres in the New Orleans area. The surge breached the levee system protecting New Orleans, flooding approximately 80% of the city. Over 1,800 people died and damage exceeded £100 billion. The disaster exposed significant weaknesses in flood protection infrastructure and emergency response systems. Following Katrina, the US invested £10 billion in improving New Orleans' flood defences, including strengthened levees, floodwalls and the world's largest storm surge barrier.

Management and Mitigation Strategies

Early Warning Systems

Early detection and warning are crucial for saving lives:

  • Tsunami Warning Systems: Networks of seismic stations, tide gauges and DART buoys that detect potential tsunami-generating events and issue alerts
  • Storm Tracking: Weather satellites, aircraft reconnaissance and computer models track storms and predict surge heights
  • Public Alert Systems: Sirens, emergency broadcasts, mobile alerts and evacuation instructions

Structural Protection Measures

Physical barriers and infrastructure can reduce impacts:

  • Sea walls, levees and flood barriers
  • Tsunami breakwaters and sea gates
  • Elevated buildings and critical infrastructure
  • Flood-resistant building designs

Natural Protection Approaches

Nature-based solutions offer sustainable protection:

  • Preservation and restoration of mangrove forests
  • Maintenance of coral reefs and sand dunes
  • Creation of coastal wetlands as buffer zones
  • Beach nourishment programs

Community Preparedness

Preparing communities is essential:

  • Evacuation plans and clearly marked routes
  • Regular drills and public education
  • Land-use planning to limit development in high-risk areas
  • Emergency supply stockpiles

💡 What to Do During a Tsunami Warning

  1. If you feel strong shaking, move immediately to higher ground
  2. Follow evacuation orders without delay
  3. Move at least 2 km inland or 30 metres above sea level
  4. Stay away from the coast until officials declare it safe
  5. If caught in tsunami waters, grab onto a floating object

💡 What to Do During a Storm Surge Warning

  1. Evacuate if instructed by authorities
  2. Move to a designated storm shelter or inland location
  3. Avoid driving through flooded areas
  4. Prepare your home by boarding windows and moving valuables to higher floors
  5. Have emergency supplies ready including food, water and medications

Future Challenges and Considerations

As we look to the future, several factors will influence storm surge and tsunami risks:

  • Climate Change: Rising sea levels will make storm surges more damaging, even from weaker storms
  • Coastal Development: Increasing population and infrastructure in coastal areas puts more people and property at risk
  • Improved Technology: Better prediction and warning systems will help reduce casualties
  • International Cooperation: Sharing data and resources across borders improves tsunami detection and warning

Understanding these coastal flooding hazards is vital for communities living in vulnerable areas. By combining early warning systems, protective infrastructure, natural buffers and community preparedness, we can reduce the devastating impacts of storm surges and tsunamis.

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