Volcanoes and Volcanic Activity Lecture Notes

Flashcards covering the definitions, types, formations, and environmental impacts of volcanoes based on the provided textbook pages.

What is the definition of a volcano?

A hole in the Earth's crust through which molten rock is pushed out.

What is the difference between magma and lava?

Magma is molten rock located under the Earth's surface, while lava is molten rock that reaches the Earth's surface.

What is the 'Ring of Fire'?

A region of earthquake and volcanic activity that surrounds the Pacific Ocean.

Where do volcanoes most commonly form in relation to tectonic plates?

Along convergent plate boundaries (where plates collide), divergent plate boundaries (where plates separate), and over hot spots.

How do hot spots create a chain of volcanoes?

A tectonic plate moves over a stationary thermal upwelling (convection current). As the plate moves, older volcanoes become inactive and move away, while the newest volcano forms directly over the hot spot.

What percentage of Earth's volcanic activity occurs along mid-ocean ridges?

More than $60\%$.

What are the characteristics of a Shield Volcano?

A large volcano with gentle slopes formed by low-viscosity basaltic lava.

What are the characteristics of a Composite Volcano?

A large, steep-sided volcano formed by explosive eruptions of andesitic and rhyolitic lava and ash along convergent boundaries.

What is a Cinder Cone volcano?

A small, steep-sided volcano that erupts gas-rich basaltic lava.

How is a Caldera formed?

It is a large volcanic depression formed when the summit of a volcano collapses or explodes due to explosive activity.

Which chemical compound primarily determines the viscosity of magma?

Silica ($SiO_2$).

How does silica concentration affect the flow of magma?

Low silica concentration results in low viscosity (flows easily like warm honey), while high silica concentration results in high viscosity (flows slowly like thick toothpaste).

What are the three main dissolved gases found in magma?

Water vapor, carbon dioxide ($CO_2$), and sulfur dioxide ($SO_2$).

Why does high-viscosity magma often lead to explosive eruptions?

Gases cannot escape easily from thick, high-viscosity magma, leading to a buildup of pressure until an explosion occurs.

What are Lahars?

Volcanic mudflows formed when thermal energy from an eruption melts snow and ice, mixing it with mud and ash.

What are the characteristics of pyroclastic flows?

Fast-moving avalanches of hot gas, ash, and rock that can travel faster than $100\,km/h$ and reach temperatures exceeding $1000\,^\circ C$.

How can volcanic eruptions impact the global climate?

Ash can block sunlight, and sulfur dioxide gas forms sulfuric acid droplets that reflect sunlight into space, both leading to a decrease in global temperatures.

What were the effects of the Mount Pinatubo eruption in 1991?

It released over $20$ million tons of gases and ash, causing global temperatures to drop by approximately $1\,^\circ C$ for a year.

What indicators do geologists use to predict volcanic eruptions?

Magma movement, changes in the volcano's shape, earthquake swarms (seismic tremors), increased gas emissions, and rising acidity in nearby groundwater.