Why in the News
On 24 October 2026, a magnitude 6.8 earthquake struck the sea near Vanuatu in the South Pacific (USGS: 02:31:28 UTC, epicentre about 203 km north-west of Port Olry, depth 16 km; the USGS PAGER system issued a green alert, indicating a low likelihood of casualties and damage). Beyond the event itself, Vanuatu's setting makes it a compact Prelims package: a Pacific island nation, a subduction zone, the Ring of Fire and tsunami science.
Vanuatu: Key Facts
- A Melanesian island nation of the South Pacific: a Y-shaped chain of four main islands and about 80 smaller islands spread over roughly 1,100 km, lying between New Caledonia and Fiji.
- Location: about 1,750 km east of Australia, about 500 km north-east of New Caledonia, west of Fiji and south of the Solomon Islands; land area 12,199 sq km; an exclusive economic zone of about 860,000 sq km (Government of Vanuatu).
- Capital Port Vila, on Efate island; the largest island is Espiritu Santo; the currency is the vatu; the official languages are Bislama, English and French.
- History: named the New Hebrides by Captain James Cook; administered from 1887 by an Anglo-French naval commission and from 1906 as an Anglo-French Condominium (joint rule); independent on 30 July 1980; a unicameral parliament of 52 members.
The Pacific Ring of Fire
- The Ring of Fire (circum-Pacific belt) is the horseshoe-shaped zone around the Pacific Ocean where the Pacific Plate meets many surrounding plates. According to the USGS, it is the most seismically and volcanically active zone in the world.
- About 90% of the world's earthquakes occur in this belt. The next most seismic region is the Alpide belt, with 5-6% of earthquakes, extending from the Mediterranean eastward through Turkey, Iran and northern India (USGS).
- The belt is roughly 25,000 miles (about 40,000 km) long and holds about 75% of the world's active and dormant volcanoes (National Geographic). It is not a single continuous ring of volcanoes, and most of its earthquakes are caused by plate movement, not eruptions.
- Vanuatu's tectonics: Vanuatu sits on the Vanuatu (New Hebrides) subduction zone. Here the Australian plate moves eastward and subducts beneath the New Hebrides plate at the New Hebrides Trench; subduction-related volcanism produced the Vanuatu archipelago, which is why earthquakes and active volcanoes are frequent there.
Tsunami: The Science
- The word: "Tsunami" is Japanese - "tsu" (harbour) and "nami" (wave). The older English term "tidal wave" is a misnomer: tsunamis have nothing to do with tides (NOAA).
- Causes: Most tsunamis are generated by large earthquakes below or near the ocean floor. Submarine or coastal landslides, volcanic eruptions, certain weather events and, very rarely, impacts of near-Earth objects can also displace the water column (NOAA).
- Deep-ocean behaviour: A tsunami's speed depends on water depth - it equals the square root of (gravity x depth). In the deep ocean a tsunami can travel faster than a jet plane, over 500 mph (800 km/h), with a wavelength of hundreds of kilometres but a height of under one metre, so ships at sea usually do not notice it passing (NOAA).
- Near the coast: In shallow water the wave slows to about 20-30 mph (30-50 km/h), its wavelength shortens and its height grows - the "shoaling" effect. The first wave is not always the largest in the series (NOAA).
- Warning systems: Deep-ocean DART buoys detect small sea-level changes and relay them to warning centres (NOAA). The Pacific Tsunami Warning Center serves the Pacific. After the 26 December 2004 Indian Ocean tsunami, India set up the Indian Tsunami Early Warning Centre (ITEWC) at the Indian National Centre for Ocean Information Services (INCOIS), Hyderabad, under the Ministry of Earth Sciences. Operational since 15 October 2007, it can detect tsunamigenic earthquakes within 10 minutes and issues advisories to Indian Ocean rim countries under the UNESCO-IOC framework.
Prelims Practice Questions
Question 1. Consider the following statements about the Pacific Ring of Fire:
1. About 90% of the world's earthquakes occur in the circum-Pacific belt
2. It is a single continuous chain of erupting volcanoes encircling the Pacific Ocean
3. After the circum-Pacific belt, the Alpide belt is the next most seismic region of the world
Which of the statements given above is/are correct?
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3
Answer and Explanation
Answer: (b). Statements 1 and 3 are correct as per the USGS: about 90% of the world's earthquakes occur in the circum-Pacific belt, and the Alpide belt (Mediterranean to northern India) is next with 5-6%. Statement 2 is wrong: the Ring of Fire is not a continuous chain of erupting volcanoes; it is a zone of plate boundaries, and most of its earthquakes are tectonic rather than volcanic.
Question 2. Consider the following statements about tsunamis:
1. In the deep ocean, a tsunami can travel at over 800 km/h while its wave height remains less than one metre
2. A tsunami gains speed as it enters shallow coastal waters
3. The word "tsunami" is Japanese and means "harbour wave"
Which of the statements given above is/are correct?
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3
Answer and Explanation
Answer: (b). NOAA states that in the deep ocean a tsunami moves at over 500 mph (about 800 km/h) with a height rarely above three feet (about one metre). Statement 2 is wrong: as a tsunami enters shallow water it slows down to about 20-30 mph, its wavelength decreases and its height increases (shoaling). Statement 3 is correct: "tsu" means harbour and "nami" means wave in Japanese.
Question 3. Consider the following statements about Vanuatu:
1. Before independence, it was administered as an Anglo-French Condominium
2. It became independent on 30 July 1980
3. It is located east of Papua New Guinea and north of Fiji
Which of the statements given above is/are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
Answer and Explanation
Answer: (a). According to the Government of Vanuatu's country profile, the islands were jointly administered by Britain and France as the Anglo-French Condominium from 1906, and full sovereignty came on 30 July 1980. Statement 3 is wrong: Vanuatu lies about 1,750 km east of Australia, north-east of New Caledonia, west of Fiji and south of the Solomon Islands.
Sources
USGS FAQs - Ring of Fire as the most seismically and volcanically active zone
about 90% of the world's earthquakes in the circum-Pacific belt
NOAA - tsunami causes, deep-ocean speed and height, shoaling, DART systems, word origin
Vanuatu Tourism Office - Espiritu Santo as the largest island
UN Permanent Mission of Vanuatu country facts (Y-shaped chain, Melanesia)
Limitations: earthquake parameters are as published by the USGS and may be revised
the 75% volcano share and the 25,000-mile extent are from National Geographic's explainer (a reputable secondary source), as the USGS pages state the 90% earthquake figure but not the volcano percentage.