Iceland: Hot Spot on Mid-Ocean Ridge

 
  • Iceland is one of the few places on Earth where a hot spot lies at the crest of a mid-ocean ridge
  • because of the hot spot, vastly more magma erupts at Iceland than at other places on the Mid-Atlantic Ridge
  • igneous activity has built a broad submarine plateau

 

  • Iceland straddles a divergent plate boundary
  • it is being stretched apart and has been cut up by faulting
  • the central part of Iceland is a narrow rift, marking the trace of the Mid-Atlantic Ridge axis, where the youngest volcanic rocks of the Island were extruded

 

 

 

 

 

 

 

  • the Iceland Basalt Plateau rises more than 3000 m above the surrounding seafloor
  • the Plateau covers about 350,000 square km.
  • about 30% of this area is above sea level
  • Iceland is geologically, very young
  • all of its rocks were formed within the past 25 million years

 

 

  • the surface of Iceland has changed radically during its brief existence
  • the forces of nature that shape and mould the Earth's surface operate faster in Iceland than in most other places
  • the rocks are shattered by frequent freeze/thaw cycles
  • winds, seas and glaciers grind down the land
  • erosion removes about a million cubic meters of land from Iceland each year
  • volcanism and sedimentation more than counterbalance this loss

 

 

  • about 70 million years ago the continental land mass began to break up along a fracture zone and a new plate boundary was formed
  • the North American plate and Eurasian plate move apart at about 2 cm/year
  • the Iceland mantle plume developed about 65 million years ago
  • the Large Igneous Province formed that includes:
    • Scotland
    • Greenland
    • Iceland

 

 

  • Iceland is located at the junction between:
    • Reykjanes Ridge in the south
    • Kolbeinsey Ridge in the north
  • the ridges represent submarine segments of the Mid-Atlantic Ridge
  • the plate boundary spreading results in the formation of wide cracks and faults that are oriented perpendicular to the spreading direction (parallel to the ridge)
  • the faults occur in swarms confined to narrow belts called volcanic zones
  • the volcanic zones are connected by transform faults known as fracture zones or, when volcanically active, volcanic belts

 

 

 

 

 

 

 

  • the center of the Icelandic mantle plume is below the northwestern part of the Vatnajokull icecap
  • it is thought to be a 200-300 km-wide cylindrical zone of highly viscous material that is hot and buoyant
  • it rises extremely slowly from depths of 400-700 km

 

 

 

 

Iceland Volcanism

 

 

 

 

  • It's not easy to determine the number of active volcanoes and or how many eruptions have occurred in history
  • the definitions of a volcano and an eruption vary
  • recent volcanic activity in Iceland shows that on average there is an eruption every three to five years
  • using the more conservative estimate this translates into about 200 eruptions in the past 1000 years
  • using this estimate, it is estimated there have been 5 million eruptions since the birth of Iceland

 

 

  • scientists have introduced the concept of volcanic systems
  • a volcanic system is a fissure swarm or a central volcano or both
  • these are surface expressions of two different types of subsurface magma-holding structures
    • a deep-seated magma reservoir
    • a shallower crustal magma chamber
  • each volcanic system is characterized by:
    • specific tectonic architecture
    • distinct magma chemistry
    • typically have a lifetime of 0.5 to 1.5 million years
    • altogether there are 30 active volcanic systems in Iceland

     

 

 

 

 

 

 

  • the fissure swarms are narrow, elongated strips (5-20 km wide and 50-100 km long)
  • they are composed of:
    •  tensional cracks
    • normal faults
    • volcanic fissures
  • they are thought to be the surface manifestations of elongated magma reservoirs at the base of the crust
  • young volcanic fissures typically appear as a row of small volcanic cones
  • fissures that erupted beneath the Ice Age glaciers occur as elongated moberg ridges

 

Moberg Ridges (Subglacial pillow lavas) on the
Reykjanes Peninsula in southwest Iceland.