NDA (II) 2025 General Ability Test · Question 116 of 147

Correct — C, Hawaiian Islands. The Hawaiian chain is the textbook example of an intraplate hotspot: it sits in the middle of the Pacific Plate over a fixed mantle plume, and as the plate drifts north-west the plume burns through it to leave a line of volcanoes — the Hawaii-Emperor seamount chain — far from any plate boundary. The other three all lie on or close to the Mid-Atlantic Ridge, the divergent boundary where the plates of the Atlantic pull apart. So the Hawaiian Islands are the one island chain not tied to a mid-oceanic ridge.

• (a)Azores Islands — The Azores sit astride the Mid-Atlantic Ridge near the Azores Triple Junction, where the North American, Eurasian and African plates meet — so this chain IS ridge-associated and cannot be the 'NOT' answer.
• (b)Ascension Islands — Ascension is a young volcanic island in the South Atlantic lying just west of the crest of the Mid-Atlantic Ridge — it is ridge-associated, not the odd one out.
• (d)Tristan da Cunha — Tristan da Cunha is a volcanic island group on or close to the Mid-Atlantic Ridge in the South Atlantic; being ridge-linked, it is not the answer to a 'NOT associated' question.

Ocean-floor volcanism comes in two main settings. At a mid-oceanic ridge — a divergent plate boundary — magma wells up as the plates separate, building islands such as Iceland, the Azores, Ascension and Tristan da Cunha along the Mid-Atlantic Ridge. A hotspot, by contrast, is a plume of hot mantle rising in the middle of a plate; as the plate drifts over the stationary plume, a line of progressively older volcanoes is left behind. The Hawaiian Islands are the classic hotspot chain, sitting deep inside the Pacific Plate rather than on any ridge.

The trick is that all four names are oceanic volcanic islands, so it is easy to lump them together. The distinguishing fact is tectonic setting: three lie on the Mid-Atlantic Ridge, but Hawaii is mid-plate. Remembering that Hawaii is the standard hotspot example immediately isolates it.

• The Mid-Atlantic Ridge is a divergent boundary; islands on or near it include Iceland, the Azores, Ascension, St Helena and Tristan da Cunha.
• The Hawaiian Islands formed over a fixed mantle hotspot in the interior of the Pacific Plate — the Hawaii-Emperor seamount chain records the plate's motion.
• A hotspot chain shows an age progression: volcanoes get older with distance from the active hotspot, unlike a ridge where volcanism follows the boundary.
• Ridge volcanism marks where plates move apart; hotspot volcanism is independent of plate boundaries.

• Do not assume every oceanic volcanic island sits on a mid-ocean ridge — hotspot chains like Hawaii lie mid-plate.
• Iceland is unusual: it lies on the Mid-Atlantic Ridge AND over a hotspot, so it is ridge-associated unlike Hawaii.

Usually framed as an odd-one-out or matching item that pairs a volcanic feature with its tectonic setting (ridge vs hotspot vs subduction zone).

• practice — not a real PYQ

  The Hawaiian island chain is the best example of which one of the following?

  • (a)Volcanism at a mid-oceanic ridge
  • (b)An intraplate hotspot chain
  • (c)Volcanism at a subduction zone
  • (d)A transform-fault island arc

  Answer(b) An intraplate hotspot chain — the islands formed as the Pacific Plate drifted over a fixed mantle plume.

• practice — not a real PYQ

  Which one of the following islands lies on the Mid-Atlantic Ridge and is also a volcanic hotspot?

  • (a)Hawaii
  • (b)Iceland
  • (c)Sri Lanka
  • (d)Madagascar

  Answer(b) Iceland — it straddles the Mid-Atlantic Ridge and sits over a mantle hotspot.