Volcano Types and Characteristics

Volcanoes are categorized into different types based on their shape, eruption style, and formation process.
- The two main categories of volcanoes discussed are shield volcanoes and composite volcanoes.

A volcano is a cone-shaped hill or mountain created by the eruption of magma, which can occur in the form of:
- Lava
- Tephra
- Other volcanic debris
The presence of a volcano indicates:
- An underlying magma source in the Earth's crust or mantle.
- Escaping gases that drive eruptions.
- Potential volcanic hazards depending on the type of volcano.
- The need for one or more eruptions to construct the volcano's cone.

The active volcanoes on Earth's surface can be represented by green triangles on a globe.
These volcanoes are predominantly found in:
- The Pacific Ocean, primarily as shield volcanoes formed at hot spots and rift systems.
- The edges of tectonic plates where chains of composite volcanoes exist, specifically above subduction zones at convergent boundaries.

Definition and Characteristics:
- Shield volcanoes have a low-angle profile, creating broad triangular landforms that resemble an overturned warrior’s shield.
- They develop primarily from a series of lava flows that emerge from vents or fissures.
Lava Properties:
- Lava flows are thin and fluid, allowing them to travel long distances along lava tubes or channels before solidifying.
- For example, the lava near the Hawaiian coast flows thinly and can travel tens of kilometers.
Examples of Shield Volcanoes:
- The largest shield volcano, Mauna Loa in Hawaii, is over 100 km across and rises more than 9 km from the sea floor, making it taller than Mt. Everest.
- Other shield volcanoes vary widely in size and may not reach such monumental dimensions.

Definition and Characteristics:
- Composite volcanoes have steep triangular profiles and are known for having more violent eruptions compared to shield volcanoes.
- These eruptions produce a mix of tephra and thick, viscous lava.
Magma Properties:
- The magma in composite volcanoes is often silica-rich, contributing to the thickness and viscosity of the lava, leading to explosive eruptions.
- Eruptions may be separated by hundreds or even thousands of years.

It is essential to understand the scale when discussing volcano classifications:
- Shield and composite volcanoes measure in tens of kilometers in width and thousands of meters in height.
- Smaller types of volcanoes such as cinder cones and lava domes generally have heights measured in hundreds of meters.
Visual Distinctions:
- Larger volcanoes, such as shield and composite types, often have surrounding forests, whereas smaller craters allow for visual identification of individual trees.

Cinder Cones:
- Small cones formed typically by a single eruption.
- Comprised of small tephra fragments produced when lava is expelled into the air and cools.
- The fragments, which contain air bubbles, are known as scoria.
Lava Domes:
- Formed by the slow emergence of thick, viscous lava at the surface, creating steep-walled, bulbous structures.
- Steep flanks can collapse, resulting in hazards like pyroclastic flows.
- Lava domes are often found within the craters of composite volcanoes but can appear in other high-silica magma environments.
Example of Lava Dome Growth:
- Time-lapse footage of lava dome growth, such as that at Mount St. Helens over three years, shows gradual movements, despite appearing fast in the footage.

A segment identified the assessment method:
- Students are shown five images of various volcano types (shield, composite, cinder cone, lava dome).
- Each image is displayed for four seconds for classification.
- Students (and a classmate named Jennifer) participate in evaluating their ability to categorize the images accurately.

The lesson concludes with a question regarding the students' confidence in distinguishing between the different volcano types.
Two learning objectives were emphasized: understanding the differences between types of volcanoes and evaluating the risks associated with volcanic hazards.