Tsunami: A Natural Hazard

The word “Tsunami” comes from Japanese — “Tsu” means harbour, and “Nami” means wave.
So literally, it means a harbour wave, because these giant waves often cause devastating impact when they reach the coast or harbour areas.

But remember — a tsunami is not a single wave.
It’s actually a series of large waves, with extremely long wavelength (often over 100 km) and long period (10–60 minutes).

These are not like normal sea waves, which are caused by wind;
Tsunamis are caused by sudden disturbances under the sea — meaning, something pushes the entire column of seawater upward or downward.

Read more about the Science of Tsunami Waves here.

⚙️ Causes of Tsunami

A tsunami is generated when there is a large, impulsive displacement of the seafloor.
The most common causes are:

1. Submarine Earthquakes
   • When the sea floor suddenly moves vertically, it displaces huge volumes of water.
   • This is the most common cause — especially near convergent plate boundaries.
2. Underwater or Coastal Landslides
   • When a large mass of rock or sediment slides into the sea, it pushes water violently.
   • This is particularly possible in the Bay of Bengal and Arabian Sea where huge sediments from the Ganga and Indus rivers are deposited.
3. Volcanic Eruptions
   • Explosive underwater volcanoes can also create tsunamis.
4. Meteorite Impacts
   • Rare, but a large meteor hitting the ocean can generate massive waves.

📊 Factors Affecting Tsunami Impact

The extent of tsunami damage depends on:

• Characteristics of the event (magnitude, depth, and location).
• Distance from point of origin (farther = less energy).
• Bathymetry (the underwater topography). Shallow coastlines amplify wave heights.

🇮🇳 Tsunami Risk in India

India’s entire coastline — both east and west — is vulnerable.
We have 7,500 km of coastline, out of which around 2,200 km is highly populated.

Historically, the Indian Ocean region has seen about 13 tsunamis in the last 300 years, three of which struck the Andaman and Nicobar Islands.

The most devastating one was the 2004 Indian Ocean Tsunami (26 December).

• Triggered by a 9.1 magnitude earthquake near Sumatra (Indonesia).
• It caused massive destruction in Tamil Nadu, Andhra Pradesh, Kerala, and A&N Islands.
• Low-lying, densely populated coastal areas suffered the worst damage.
• Natural barriers like mangroves, sand dunes, and coastal forests helped reduce impact — wherever they existed.

Hence, conserving coastal ecosystems becomes a key natural mitigation strategy.

🧱 NDMA Guidelines for Tsunami Management in India

The National Disaster Management Authority (NDMA) has issued detailed guidelines focusing on six major components — let’s go one by one.

1️⃣ Tsunami Risk Assessment and Vulnerability Analysis

Before we can manage the risk, we must measure it.

• NDMA recommends mapping of tsunami-prone areas based on:
  • Coastal land use
  • Elevation
  • Bathymetry (sea depth)
• Modeling and simulation are used to predict:
  • Time of arrival of waves
  • Run-up height (how far the water will rise on land)
• The Indian Naval Hydrographic Department (INHD) provides accurate bathymetric data to prepare inundation maps (showing potential flood extent).

2️⃣ Tsunami Preparedness

Preparedness is all about early warning and communication.

• Real-Time Seismic Monitoring Network (RTSMN) – 17 stations set up by IMD to detect undersea earthquakes.
• Bottom Pressure Recorders (BPRs) – measure changes in sea pressure caused by tsunami waves.
• National Data Buoy Programme (NIOT) – maintains data buoys to protect and monitor ocean sensors.
• Tsunami Bulletins & Warning Systems – timely alerts for authorities and the public.
• Public Awareness Measures:
  • “Tsunami Escape Route” signboards in coastal areas.
  • Frequent awareness campaigns via TV, radio, and community meetings.

3️⃣ Structural Mitigation Measures

These are physical or engineering measures to minimize impact.

• Cyclone/Tsunami Shelters near coastal villages.
• Sand Dunes & Seaweed Dykes to reduce wave force.
• Mangrove and Coastal Forest Plantation as natural bio-shields.
• Sea Walls, Coral Reefs, and Breakwaters to cushion wave energy.
• Bio-Shield Zones – narrow green belts along coastlines used for awareness and protection.
• Retrofitting Vulnerable Buildings and identifying safe Tsunami Shelters for evacuation.

👉 Example:
The M.S. Swaminathan Research Foundation developed local knowledge centres in Puducherry to train people and communicate warnings — a successful model of community-based disaster preparedness.

4️⃣ Regulation and Enforcement (Techno-Legal Regime)

Because planning and enforcement are as important as engineering.

• Strict implementation of Coastal Regulation Zone (CRZ) Rules — especially within 500 m of the high-tide line.
• Adoption of Model Techno-Legal Framework developed by the Ministry of Home Affairs (MHA) for:
  • Tsunami-safe land use zoning
  • Proper design and construction practices
  • Optimum utilization of land in coastal regions.

5️⃣ Emergency Tsunami Response

The community is the first responder — always remember this.

NDMA recommends:

• Intensive public awareness and mock drills.
• Involvement of Self-Help Groups (SHGs), NGOs, CBOs in rescue operations.
• Immediate deployment of boats, helicopters, and rescue teams for people trapped in inundated areas.
• Indian Navy plays a crucial role:
  • During the 2004 tsunami, naval ships conducted rescue, re-charted sea routes, and provided medical aid and new bathymetric data.

6️⃣ Ensuring Implementation and Capacity Building

Implementation must be continuous — not just post-disaster.

• Capacity building for local administration and communities (“cutting-edge level”).
• Training programs for fishermen, coast guards, port authorities, district officials, etc.
• Regular mock drills to test disaster management plans.

The Indian Tsunami Early Warning System (ITEWS) was developed jointly by:

• Department of Space (DoS)
• Department of Science and Technology (DST)
• Council of Scientific and Industrial Research (CSIR)

It includes:

• Real-time network of Seismic Stations, Tide Gauges, and BPRs
• Decision Support System for scenario modeling and vulnerability mapping
• Capability to detect tsunamigenic earthquakes within 10 minutes of occurrence.

🧮 Modeling and Forecasting Tools

• Tsunami N2 Model – customized by ICMAM and INCOIS.
  It predicts:
  • Possible surge height
  • Extent of seawater inundation
    Used for evacuation planning, infrastructure design, and land-use control in vulnerable zones.

⚠️ Existing Challenges in Tsunami Risk Management

1. Lack of detailed paleo-tsunami studies (study of ancient tsunami deposits).
2. Inadequate high-resolution bathymetric data for accurate modeling.
3. Low community awareness and poor participation in preparedness.
4. Weak documentation of traditional coastal knowledge.
5. Limited local involvement in disaster response and mitigation planning.