Geological Heritage of St. Mary’s Island Cluster in News
Analysis
Introduction
The Geological Heritage of St. Mary’s Island Cluster, located off the coast of Udupi, Karnataka, has been submitted by the Permanent Delegation of India to UNESCO to the Tentative List on 27 August 2025 under Criterion (viii). The site represents a rare and scientifically significant example of columnar jointing in rhyolitic lava, offering crucial insights into plate tectonics and continental drift.
Location and Physical Setting
The St. Mary’s Islands consist of a chain of four small islands extending in a NNW–SSE direction (~6 km) off the coast near Malpe:
- Coconut Island
- North Island
- Darya Bahadurgarh Island
- South Island
A rocky outcrop known as Middle Rock lies between Coconut and North Island. The islands are located near Malpe on the western coast of India.
Geological Significance
The site is globally important for its spectacular columnar joints, which are:
- Formed due to cooling and contraction of lava
- Typically polygonal (20–25 cm diameter columns)
- Vertically oriented, indicating absence of post-magmatic tilting
Unique Geological Features
- Rocks are composed of fine-grained porphyritic rhyolite and rhyodacite
- Presence of granophyric texture, one of the most striking igneous textures in India
- Formation linked to India–Madagascar separation (~85–88 million years ago)
Unlike most columnar joint formations (which are basaltic), this site is rhyolitic, making it geologically rare at a global level.
UNESCO Criterion (viii): Geological Importance
The site provides critical evidence of:
- Late Cretaceous volcanic activity
- Breakup of Gondwana (India–Madagascar rifting)
- Plate tectonics and continental drift theory
The columnar joints developed similarly to:
- Mud cracks formed by shrinkage during drying,
but here due to cooling of molten lava
Palaeomagnetic studies from the site contribute to:
- Understanding continental rifting processes
- Reconstruction of India’s geological past
Scientific and Educational Value
The site holds significance as:
- A geochronological archive (~88 million years old)
- A palaeomagnetic reference point
- A natural laboratory for studying:
- Volcanism
- Plate tectonics
- Igneous rock formation
It also supports geotourism and public engagement with Earth science due to its visually striking geometry.
Integrity and Protection
- Declared National Geological Monument (1978) by Geological Survey of India
- Protected under Coastal Regulation Zone (CRZ)
- Naturally preserved due to offshore location
Emerging Threats
- Microplastic pollution (0.218 particles/L observed)
- Tourism and fishing-related anthropogenic pressures
Comparative Global Significance
| Site | Location | Composition | Key Difference |
|---|
| Giant’s Causeway | Northern Ireland | Basalt | Basaltic vs rhyolitic columns |
| Fingal’s Cave | Scotland | Basalt | Cave structure vs open island |
| Devils Postpile | USA | Basalt | Inland vs coastal tropical setting |
St. Mary’s Islands stand out due to:
- Rhyolitic composition (rare globally)
- Association with Gondwana breakup
- Accessible coastal island geomorphology
Static Part
UNESCO World Heritage Framework
Prepared by: UNESCO World Heritage Centre
- Function: Identification and conservation of natural and cultural heritage
- Maintains Tentative List and World Heritage List
Geological Survey of India
- Declared the site as National Geological Monument (1978)
- Role: Documentation and conservation of geological heritage in India
Updated - 28 Aug 2025 News Source: UNESCO World Heritage Centre