Volcanoes

Volcanoes

Definition and Basic Concepts

• Volcanoes occur when molten rock, referred to as magma, reaches the Earth's surface, at which point it is called lava.
• There are two primary types of volcanic eruptions:
  • Vent Eruptions: Eruptions that occur through a singular opening.
  • Fissure Eruptions: Eruptions that occur through cracks in the Earth's surface.
• It is estimated that there are between 30-60 volcanic eruptions globally each year.

Structure of a Volcano

1. Active Volcanoes

   • Defined as a volcano that has erupted recently and is expected to erupt again.
   • Example: Mt. Etna, Italy.

2. Dormant Volcanoes

   • Defined as a volcano that has not erupted in recent times but has a likelihood of future eruptions.
   • Example: Yellowstone, USA. Though it has not erupted for about 700,000 years, it still shows signs of activity.

3. Extinct Volcanoes

   • Defined as a volcano no longer capable of erupting.
   • Example: Mt. Slemish, Co. Antrim.

Types of Volcanic Emissions

Lava

• Lava Types:

  • Acidic Lava:

  • High silica content leading to high viscosity.

  • Commonly found at destructive plate boundaries during subduction, where one plate melts.

  • Temperature when emitted: approximately 800°C.

  • Moves slowly and solidifies quickly.

  • Often results in explosive eruptions.

  • Example: Stratovolcanoes formed by layering eruptions (e.g., Mt. St Helens).

  • Basic Lava:

  • Low silica content (less than 55%).

  • Commonly found at constructive plate boundaries where plates separate.

  • Temperature when emitted: approximately 1200°C.

  • Low viscosity allows for travel over great distances.

  • Rarely results in explosive eruptions.

  • Example: Muana Loa, Hawaii.

Pyroclastic Flow

• One of the deadliest volcanic impacts, occurring at destructive plate boundaries during explosive eruptions.
• Comprises dense material that races down the volcano's slopes, containing tephra, which consists of:
  • Pumice (lava mixed with ash, creating air bubbles).
  • Ash.
  • Gas and water vapor.
• Speeds can reach up to 600 km/h with temperatures inside the ash cloud reaching up to 700°C.
• Notable event: Eruption of Mt. Vesuvius in AD 72, which covered Pompeii in ash, resulting in multiple fatalities.

Gasses

• Volcanoes play a crucial role in sustaining life on Earth by releasing essential gases such as:
  • Sulfur
  • Carbon dioxide
  • Chlorine
• Water Vapour:
  • During subduction, seawater can be dragged into the mantle, causing it to turn into water vapour.
  • Following an eruption, this can lead to torrential rainfall, creating landslides or lahars.

Distribution of Volcanoes

• Volcanoes are not randomly distributed; their locations often correspond to specific geological factors.
• Most volcanoes are found at:
  • Plate boundaries (especially along the Pacific Ring of Fire).
  • Hotspots.

Divergent Volcanoes

• Occur at constructive plate boundaries where two plates pull apart due to convection currents.
• Allow low silica content lava to rise, resulting in fissure eruptions.
• Characterized by less explosive eruptions.
• Commonly form underwater at mid-ocean ridges, producing pillow lava.
• Example: Eyjafjallajökull, Iceland.

Convergent Volcanoes

• Formed when two plates collide, resulting in subduction of the heavier plate below the lighter.
• Creates a magma chamber as melting occurs, which can lead to explosive eruptions from rising magma.
• Characterized by stratovolcanoes with steep sides due to alternating layers of lava accumulation.

Hotspot Eruptions

• Occur without plate boundaries.
• Superheated magma plumes rise to the surface, generating lava flow gently from the vent.
• Form shield volcanoes with broad bases and gentle slopes.
• Example: Galapagos Islands or Hawaii.

Volcanic Landforms

Extrusive Landforms

1. Volcanic Cones

   • Common features associated with volcanic activity, varying in structure and composition.
   • Stratovolcanoes:
     • Formed from earth’s explosive and gentle eruptions leading to layers of pyroclastic material.
     • Example: Mount Fuji, Japan.
   • Cinder Cones:
     • Smallest volcano type, typically under 300m.
     • Usually erupt only once, leading to destruction of their structure.
   • Shield Volcanoes:
     • Formed from gentle eruptions, with expanded gently sloping surfaces.
     • Example: Muana Loa, Hawaii.

2. Lava Plateaus

   • Formed through extensive lava floods that solidify.
   • Example: Antrim-Derry Plateau established about 60 million years ago by the separation of the Eurasian Plate and North American Plate.
   • Formation of hexagonal basalt columns, like the Giant's Causeway.
   • Example: Mt. Slemish, Co. Antrim.

Intrusive Volcanic Landforms

• Result from cooling of volcanic material within the Earth’s crust.

1. Batholiths:

   • Large regions of igneous rock formed when magma cools beneath the crust.
   • Example: Leinster Batholith, Ireland.
   • Formed more than 400 million years ago from the collision of plates and the subsequent cooling of magma.

2. Sills:

   • Horizontal layers of granite formed when magma cools between sedimentary layers.
   • Example: Slieve Gullion, Co. Armagh.

3. Dykes:

   • Vertical layers of granite formed from magma ascending through the crust.

4. Laccoliths:

   • Formed when magma intrudes between sedimentary layers, creating upward domes of granite.

5. Lopoliths:

   • Created similarly to laccoliths but with magma pushing downward to form bowl-like structures.

Prediction of Volcanoes

• Indicators of an impending eruption include seismic activity and ground deformation.

• Seismic Monitoring:

  • Seismometers and Seismographs detect earthquakes caused by magma movement.
  • Positioned within 20 km of a volcano's vent for effective monitoring.

• Ground Deformation Monitoring:

  • Electronic Distance Measurement (EDM):
    • Measures horizontal movements by sending laser signals to reflectors.
  • Tiltmeters:
    • Measure changes in slope of a volcano, using water bubbles to detect even slight shifts.
  • GPS technology:
    • Monitors changes in shape of volcanoes.
  • Satellite radar:
    • Provides visual monitoring of volcanic deformation over time.

• Gas Emission Monitoring:

  • Carbon dioxide (CO2) sensors assess gas release.
  • Example: Lake Nyos incident (1986) where carbon dioxide buildup resulted in significant fatalities.

• Historical Records:

  • Consulting past eruption histories aids in predicting future volcanic activity.

Positive Impacts of Volcanoes

Creation of New Land

• Volcanic processes aid in land formation through lava cooling and accumulation.
• Example:
  • Japan: Experienced new land emergence in November 2013 due to volcanic activity.
  • Surtsey, an island formed between 1963-1967 as the result of underwater eruptions.

Creation of Fertile Soils

• Volcanic soils, rich in nutrients from ash and lava breakdown, contribute to agricultural productivity.
• Example: Bay of Naples benefits from volcanic deposits enriching agricultural land.

Tourism

• Volcanic landscapes attract tourism, boosting local economies.
• Case study: Iceland, where volcanic features have increased tourist numbers significantly.
• Attractions include hiking volcanic mountains, geothermal sites like Blue Lagoon Spa.

Geothermal Energy

• Iceland utilizes geothermal energy due to its volcanic geology.
• Provides 26% of national energy needs; 89% of heating/electricity for locals.
• Geothermal resources stimulate economic growth through power generation and tourism.

Negative Impacts of Volcanoes

Death and Destruction

• Example: Nevada del Ruiz eruption causing the Armero tragedy leading to 23,000 fatalities due to a lahar.
  • Lack of effective evacuation procedures and communication exacerbated casualties.

Disruption to Air Traffic

• Ash and debris can interfere with aircraft safety, leading to flight cancellations.
• Example: Eyjafjallajökull eruption in 2010, canceling flights for over 8 million passengers across 20 countries.