Describe the shape of the volcanic cone formed from the following types of volcanic emission:
A.high temperature magma.
B.low amount of gas magma
C.high silica content magma
The Correct Answer and Explanation is :
Shape of Volcanic Cones Based on Volcanic Emissions
- High Temperature Magma:
- Cone Shape: Broad and gently sloping (shield volcano).
- Explanation: High-temperature magma is typically low in viscosity and rich in basaltic composition. This magma flows easily over long distances before solidifying, forming a broad, gently sloping shield-like structure. Examples include the Mauna Loa and Kilauea volcanoes in Hawaii. These shield volcanoes are characterized by large surface areas and relatively low heights compared to their base width.
- Low Amount of Gas Magma:
- Cone Shape: Dome-shaped (lava dome).
- Explanation: Magma with a low amount of gas does not produce significant explosive eruptions. Instead, it tends to emerge slowly and build up in the vicinity of the vent. This results in a steep-sided, dome-like structure. The viscosity of the magma plays a role here as well; even if it’s not highly viscous, the absence of gas pressure prevents the formation of broader structures. Lava domes are often smaller compared to shield volcanoes and stratovolcanoes but can become quite steep due to the slow, continuous extrusion of magma.
- High Silica Content Magma:
- Cone Shape: Steep and conical (stratovolcano or composite volcano).
- Explanation: High silica content magma (felsic magma) is highly viscous and traps gases, leading to explosive eruptions. These eruptions deposit alternating layers of ash, pumice, and hardened lava, forming a steep and conical structure known as a stratovolcano. Due to its viscosity, the lava flows are short and contribute to the buildup of steep slopes. Examples include Mount St. Helens in the USA and Mount Fuji in Japan.
Summary
- High temperature magma: Broad shield volcanoes.
- Low gas magma: Dome-shaped lava domes.
- High silica content magma: Steep stratovolcanoes.
The interplay between magma viscosity, temperature, and gas content determines the eruption style and cone shape.