Lecture Notes: Volcanic and Tectonic Activity

Introduction

• Speaker: Darren Gage
• Location: Summit of Mount Narahoe
  • Elevation: 2291 metres
  • Third highest mountain in the North Island
  • Part of the Tongariro complex
  • Last erupted in 1975

Geological Background

• Volcano Formation
  • Involves processes deep within the Earth

Earth's Internal Structure

• Core
  • Metallic, composed of iron and nickel
  • Located 6360 km below surface
  • Temperatures over 5500°C
  • Liquid inferred by seismic wave behavior
• Mantle
  • Surrounds the core, 2890 km below surface
  • Composed of silicate rocks, rich in magnesium and iron
  • Asthenosphere (outer mantle): semi-molten rock with convection currents

Plate Tectonics

• Lithosphere/Crust
  • Comprised of tectonic plates floating on the mantle
  • Plates move due to convection currents
• Types of Tectonic Plates
  • Oceanic Crust: basalt rock, 5-10 km thick
  • Continental Crust: granitic, sedimentary, metamorphic rocks
    • Thicker (35-40 km, up to 70 km under mountains)

Plate Movements

• Convergent Margins
  • Plates move towards each other
  • Can lead to subduction zones or continental collisions
• Divergent Margins
  • Plates move apart, forming mid-ocean ridges
  • New oceanic crust forms through seafloor spreading
• Transform Margins
  • Plates slide past each other
  • Cause earthquakes

Subduction Zones

• Location: East of New Zealand's North Island
  • Pacific Plate subducting under the Indo-Australian Plate
• Characteristics: Deep marine trenches, fold mountain ranges
  • Example: Kermadec Trench, Kea Manoas

Volcanic and Seismic Activity

• Ring of Fire
  • Pattern of activity around the Pacific
• Hotspots
  • Localized heat sources under the crust, not at plate boundaries
  • Example: Auckland volcanic field
    • Contains ~60 volcanoes, including Rangitoto Island, One Tree Hill, Mount Eden

Notable Examples

• Himalayas
  • Formed by collision of Indian and Eurasian Plates
• Mid-Atlantic Ridge
  • North American Plate moving away from Eurasian Plate
  • Volcanically active Iceland formed along ridge
• Alpine Fault in New Zealand
  • Transform boundary causing earthquakes
  • Northwest Nelson separated from southern New Zealand

These notes capture the main concepts from the lecture on the formation and movement of tectonic plates, volcanic activity, and related geological phenomena.