APAC Work: Geography

Explain the characteristics and spatial distribution of the following hazards using at least two specific examples. [10 marks]

DURATION

Volcanic eruptions vary in strength and can last anywhere from less than a day to thousands of years. The Stromboli in the Mediterranean, for example, has been erupting for over 2,400 years. An eruption will usually last until the magma has depleted, or until the gas inside the chamber is low enough so that the gas is no longer trying to escape.

Mt. Vesuvius: Extremely varied throughout history
Krakatoa: Extremely varied throughout history


MAGNITUDE

The Volcanic Explosivity Index or VEI is used to measure the intensity of volcanic eruptions. The scale is dependent on how much volcanic material is thrown out, the height of it, and the duration of the activity. Eruptions have 8 classifications, from 0 or non-explosive to 8 or mega-colossal.

Mt. Vesuvius: typically mega-colossal
Krakatoa: typically colossal to mega-colossal


PREDICTABILITY

Volcanoes are difficult to precisely predict but there are usually various warning signs that suggest impending eruptions. Scientists monitor seismicity rates, quake activity, and ground deformation. They are usually able to predict volcanic eruptions weeks in advance, giving local populations sufficient time to evacuate.

Mt. Vesuvius: Constantly monitored due to the unusually high density of surrounding population.
Krakatoa: Early eruptions were not predicted, but current volcanic activity is monitored heavily.


REGULARITY

Volcanoes are typically categorized according to various things like duration, lava flow, cause, magnitude, etc. Some common types of volcanic eruptions include Hawaiian Eruptions, Strombolian Eruptions, Vulcanian Eruptions, Plinian Eruptions, Lava Domes, and Surtseyan Eruptions.

Mt. Vesuvius: Plinian Eruptions
Krakatoa: Plinian Eruption, more recently Strombolian Eruptions


FREQUENCY

Of the 500 or so active volcanoes across the world, around 10 are erupting every day. But for the most part, they are very small, contained, and harmless. From time to time however, we get major eruptions that are large enough to destroy properties and even take lives.

Mt. Vesuvius: Highly active, with multiple historical accounts of catastrophe.
Krakatoa: Very highly active and dangerous with multiple recent minor eruptions, but catastrophic eruptions in history.


SPEED OF ONSET

Although volcanic eruptions can currently be predicted days or even weeks in advance, the onset of the eruption itself varies considerably. They may occur suddenly or gradually.

Mt. Vesuvius: Varies considerably
Krakatoa: Varies considerably


SPATIAL DISTRIBUTION

Volcanoes are found along destructive (convergent) plate boundaries, constructive (divergent) plate boundaries, and at various hot spots in the earth’s surface. The Ring of Fire is a famous volcanic chain that surrounds the Pacific Ocean. More than half of the world’s active volcanoes above sea level are a part of this ring.

Mt. Vesuvius: Gulf of Naples, Italy
Krakatoa: Sunda Strait, Indonesia