Understanding Kallakkadal: Why the 'Thief Sea' Causes Sudden Flooding in Kerala

What is Kallakkadal?

Kallakkadal, often translated as the 'thief sea,' refers to a phenomenon where seawater suddenly rises, creating high, rough waves that can unexpectedly inundate coastal areas. Unlike a tsunami, which is typically triggered by seismic activity, Kallakkadal is a swell surge phenomenon caused by high-energy waves traveling across vast distances of the ocean.

In late September 2026, this phenomenon triggered a red alert along the coasts of Kerala, southern Tamil Nadu, and Lakshadweep. The event was driven by high-energy swell waves that originated approximately 10,000 km away in the southern Indian Ocean on September 20, 2026, gradually propagating toward the northern Indian Ocean [1].

The Science Behind the Surge

The September 2026 event was characterized by "long-period swells," which are waves that maintain their energy over long distances. According to the Indian National Centre for Ocean Information Services (INCOIS) and the Kerala State Disaster Management Authority (KSDMA), these waves had a period of 20 to 24 seconds and reached heights of up to 1.5 metres [1].

When these high-energy swells coincide with high-tide conditions, they can cause significant coastal flooding and sea erosion, particularly in low-lying areas. This combination is what leads to the "sudden rise" of seawater that characterizes the Kallakkadal effect [2].

Impact and Safety Warnings (September 2026)

From September 26 to September 28, 2026, authorities issued strict advisories to protect coastal residents and tourists. The red alert specifically targeted the entire Kerala coast, as well as districts in Tamil Nadu including Kanyakumari, Ramanathapuram, Thoothukudi, and Tirunelveli [2].

Key safety measures implemented during this period included:

• Suspension of Activities: All recreational activities, beach tourism, and fishing were suspended until the warning was withdrawn.
• Maritime Caution: Fishermen were advised not to operate small vessels close to shore and to anchor boats at a safe distance from one another to prevent collisions [1].
• Evacuation: People in vulnerable, low-lying regions were advised to move to safer locations as directed by local authorities [2].

High-Risk Coastal Stretches

The KSDMA highlighted specific areas requiring extreme caution, including Thiruvananthapuram (Kappil to Pozhiyoor), Kollam (Alappad to Edava), and Alappuzha (Chellanam to Azhikkal Jetty), among others [2].