Volcanic Ash: Introduction

• Volcanoes — Understanding the Source
• Eruption Dynamics
• Volcanic Regions
• Eruption Types
• Classification of Volcanic Eruptions
  • Hawaiian Eruptions
  • Strombolian Eruptions
  • Vulcanian Eruptions
  • Plinian Eruptions
  • Questions
• Eruption Frequency and Size
• Volcanic Hazards
  • Tephra
  • Pyroclastic Flows
  • Lahars
  • Lava Flows
  • Volcanic gases
  • Tsunami
  • Questions
• Summary
• References/Bibliography

Summary

This module explored the geologic elements involved in explosive volcanic eruptions. Specifically, the major fault lines and currently active volcanoes are located in the Ring of Fire — defined by a nearly continuous series of oceanic trenches, island arcs, and volcanic mountain ranges and/or boundaries of several plates. Not all volcanoes occur along the Ring of Fire, however, as there are several other areas in the world with active volcanoes, like Iceland and Italy.

Volcanoes come in different shapes and sizes, however, there are several common features. Each volcano has a shallow "plumbing system” that may include a magma chamber that is connected to the surface by a conduit system.

During an eruption, magma rises through more than one crack; some of the magma pushes up the strata layers while other magma moves to the top opening(s) of the volcano. The raised opening that emits magma is called the cone. The crack that reaches to the top of the cone is called the Central Vent. Along with the magma, the volcano emits a cloud of tephra.

Volcanic eruptions form a continuum from small quiet affairs to large explosive catastrophes. Volcanologists have developed many schemes to categorize eruptions.  The meteorologist should be familiar with these four eruption types and related ash dispersion patterns:

• Hawaiian — this eruption produces little volcanic ash
• Strombolian — this eruption is short-lived and the ash is not ejected to great heights
• Vulcanian — this eruption produces large quantities of ash that can be dispersed for miles downwind
• Plinian — this eruption produces large quantities of ash that can be ejected high into the stratosphere and circle the globe

Different volcanic eruptions can produce different hazards. These are some of more important hazards and the dangers they pose:

• Tephra — covers broad swaths of land, destroys mechanical equipment, and creates health issues
• Pyroclastic Flows — rapidly burn and destroy everything in their path
• Lahars — destroys structures, covers the land with debris and mud, and may alter rivers and streams
• Lava Flows — slowly burn and destroy everything in their path
• Volcanic Gases — associated with large explosive eruptions; lead to acid rain in the immediate vicinity and possible short-term climatic changes

In future modules, you will learn about the tools used to monitor volcanoes and their eruptions, as well as the models used in forecasting ash dispersion. You will also become familiar with the impacts to aviation, climate, maritime operations and society.