Why In News?

The Indian National Centre for Ocean Information Services (INCOIS) issued coastal warnings and red alerts along the shorelines of Kerala, south Tamil Nadu, and Lakshadweep due to severe Swell Surge (Kallakkadal) events.

 

What is the Swell Surge Phenomenon?

A swell surge, locally called "Kallakkadal" in Kerala (meaning "sea that has come as a thief" in Malayalam), is a sudden inundation of the coast by high, long-period ocean waves that arrive without local warning signs such as strong winds or storms.

 

It is caused by swell waves: long-wavelength, long-period waves generated by distant storms or low-pressure systems, which travel thousands of kilometres across the ocean before striking the coast.

 

Unlike storm surges, swell surges occur even under clear skies and calm local weather, making them deceptively dangerous.

 

Mechanisms of Formation

Distant storm generation: A low-pressure system or storm forms over the South Atlantic or southern Indian Ocean, generating strong winds over open water.

 

Long-distance travel: These winds create swells — organised, long-period waves — that travel across 8,000–10,000 km of open ocean with minimal energy loss.

 

Coastal interaction: As swells reach the shallow continental shelf near the Indian coast, wave energy gets compressed, increasing wave height sharply.

 

Amplification by tides: If swell arrival coincides with high tide, the surge effect intensifies, causing water to push further inland.

 

No local wind signature: Because the triggering storm is thousands of km away, local winds remain calm, so the phenomenon strikes without visible warning.

 

Key Characteristics

Sudden onset — occurs abruptly, often during early morning or night hours, catching coastal communities unaware.

 

No storm link locally — occurs under clear, calm weather, unlike cyclonic storm surges.

 

Short duration but high intensity — lasts 12 to 48 hours.

 

Wave heights — generally range from 0.5 m to 2.2 m, though a 2024 event recorded swell waves up to 11 metres off Kerala's coast.

 

Seasonal pattern — most frequent during pre-monsoon (April–May) and southwest monsoon months, linked to Southern Ocean storm activity.

 

Localised impact — affects low-lying coastal stretches, especially unprotected beaches and fishing hamlets, more than the open sea.

 

Impact

Coastal flooding and inundation of low-lying residential areas, particularly in Thiruvananthapuram, Kollam, Alappuzha, and Thrissur districts of Kerala.

 

Damage to fishing infrastructure — boats, nets, and gear are frequently destroyed as waves surge without warning.

 

Coastal erosion, undermining sea walls, roads, and property near the shoreline.

 

Disruption of livelihoods — fishermen are barred from venturing into the sea, halting economic activity for the alert period.

 

Suspension of tourism — beach and nearshore recreational activities are shut down during red/orange alerts.

 

Displacement — coastal residents are advised to temporarily evacuate low-lying zones.

 

How Swell Surge Differs from a Tsunami

Feature

Swell Surge (Kallakkadal)

Tsunami

Trigger

Distant storms/low-pressure systems generating wind-driven swells

Undersea earthquakes, volcanic eruptions, or landslides

Wave type

Wind-generated long-period swell waves

Seismic sea waves caused by sudden displacement of water column

Warning time

Hours to 1–2 days (trackable via swell forecasting)

Often minutes — very limited warning

Local weather signature

None — occurs in calm, clear weather

None — but linked to seismic activity, not weather

Wave height at coast

Usually 0.5–2.2 m (extreme cases up to 11 m)

Can exceed 10–30 m in extreme cases

Duration

12–48 hours, intermittent surging

Few hours, but waves arrive in successive series

Nature of damage

Gradual inundation and erosion

Sudden, violent inundation, structural destruction

 

 

 

Source: HINDUSTANTIMES

 

 

 

PRACTICE QUESTION

Q. With reference to the 'Kallakkadal' phenomenon, consider the following statements:

1. It is caused by undersea seismic disturbances along tectonic plate boundaries.

2. It occurs along coastal areas without any noticeable local atmospheric change or storm warning.

3. The term has been officially recognized for scientific usage by UNESCO.

Which of the statements given above are correct?

(a) 1 and 2 only

(b) 2 and 3 only

(c) 1 and 3 only

(d) 1, 2, and 3

Answer: (b) 2 and 3 only

Explanation: 

Statement 1 is incorrect: The Kallakkadal phenomenon is not caused by undersea seismic disturbances or tectonic activity (which cause tsunamis). Instead, it is caused by ocean swell waves generated by distant storms or severe weather systems (such as hurricanes or high winds) thousands of kilometers away. 

Statement 2 is correct: It strikes coastal regions suddenly and unpredictably without any local atmospheric changes, strong local winds, or prior storm warnings.  

Statement 3 is correct: The scientific term Kallakkadal (combining the Malayalam words for thief and sea) was formally approved and recognized for international scientific usage by UNESCO in 2012.