Volcanic Hazards — Reading Comprehension

Volcanic hazards are powerful natural events that can cause destruction to people, property, and the environment. When a volcano erupts, it releases various materials and forces, each creating different types of risks. Understanding these hazards helps scientists, emergency planners, and communities reduce damage and save lives. The dangers posed by volcanic activity depend on factors like the type of eruption, the materials involved, and how far people are from the volcano.

Lava Flows and Pyroclastic Flows
One common volcanic hazard is the lava flow. Lava is molten rock that erupts from a volcano and moves slowly across the ground, often at speeds of less than 10 km/h. While lava flows can destroy everything in their path—including homes, roads, and forests—they usually move slowly enough for people to evacuate safely. In contrast, pyroclastic flows are extremely dangerous. These are fast-moving clouds of hot gas, ash, and rock that can travel at speeds over 100 km/h and reach temperatures up to 700°C. Pyroclastic flows are unsurvivable for anyone caught in their path, as demonstrated by the famous eruption of Mount Vesuvius in 79 CE, which buried the city of Pompeii under a thick layer of ash and hot debris.

Tephra, Lahars, and Volcanic Gases
Volcanoes also eject tephra, which includes all sizes of airborne volcanic material, from fine ash to large rocks. Tephra can collapse roofs, bury crops, and disrupt aviation because ash can damage jet engines. Breathing volcanic ash can also cause health problems. Another hazard is the lahar, a fast-moving mudflow formed when volcanic ash mixes with water, such as from rain or melting snow. Lahars can travel long distances down river valleys, burying entire communities. The 1985 eruption of Nevado del Ruiz in Colombia caused a lahar that killed 23,000 people. Volcanic eruptions also release volcanic gases such as carbon dioxide and sulfur dioxide. Carbon dioxide, being heavier than air, can collect in low-lying areas and cause suffocation, while sulfur dioxide can create acid rain and worsen respiratory illnesses.

Tsunamis and Secondary Hazards
Volcanoes near coastlines can trigger tsunamis (large ocean waves) if parts of the volcano collapse or if a caldera forms suddenly. Tsunamis can flood coastal areas and cause loss of life far from the eruption site. Volcanic eruptions can also have secondary hazards, such as climate changes. For example, large eruptions can send ash and gases into the atmosphere, blocking sunlight and causing global temperatures to drop. This can lead to crop failures and famine, affecting people around the world, not just near the volcano.

Each volcanic hazard has different effects depending on distance from the volcano, local geography, and weather conditions. By studying past eruptions, scientists can better predict and prepare for future events, helping to protect lives and property.

Interesting Fact:
The 1815 eruption of Mount Tambora in Indonesia caused “the year without a summer” in 1816, leading to widespread crop failures and hunger in North America and Europe.

Which volcanic hazard is usually slow enough for people to evacuate safely?

What happened to the city of Pompeii during the eruption of Mount Vesuvius?

Tephra can cause which of the following hazards?

What is a lahar?

What does the word 'secondary hazards' mean in the passage?

Which volcanic gas is heavier than air and can cause suffocation?

Why are pyroclastic flows more deadly than lava flows?

If a volcano near the ocean collapses, what hazard can it create far from the eruption site?

True or False: Lahars can travel long distances down river valleys and bury entire communities.

True or False: All volcanic hazards can be predicted with complete accuracy.