Lecture 5: Volcanos Flashcards
What are the 3 products of volcanic eruptions?
- Magma (molten rock)
- Volatiles (gases)
- Pyroclasts (airborne material)
What are the factors that affect the eruption style, and what do they control?
- composition of the magma
- temperature of the magma
- dissolved gases in the magma
They control the viscosity of the magma
What is the magma composition partially related to?
It’s related to the degree of partial melting of asthenosphere rock.
What happens with convergent boundaries?
Magma is produced by hydration melting (water driven by subjecting oceanic plate lowers melting point of asthenosphere rock)
- intermediate to felsic magma
What are divergent boundaries?
Magma produced by decompression melting (melting of high temperature asthenosphere rock)
- mafic magma
What are intrastate hotspots?
Discrete heat plumes that locally melt high temperature asthenosphere rock
- mafic magma
What is the main texture of volcanic igneous rocks
Aphanatic (Glassy) texture due to the rapid cooling at Earth’s surface.
What are the three most important volcanic rocks?
Basalt (mafic)
Andesite (intermediate)
Rhyolite (felsic)
What are the special textures of volcanic rocks?
- Porphyritic
- Glassy
- Vesicular
What is a porphyritic texture?
The rock has large crystals (easy to physically see the particles). This was due to slow cooling of magma.
What is a glassy texture?
When the magma cools immediately, the crystals do not have time to form.
What is vesicular texture?
When the rock has air bubbles within it, the volatiles were trapped in the rock.
What makes a volcano more explosive?
Higher volatile content and higher viscosity.
What are the 3 types of volcanos?
- shield (small bump, almost looks like flat land)
- composite cone (typical volcano )
- cinder cone (2 bumps)
What is a caldera?
When the top of a volcano caves, in it produces a caldera.
What are pyroclastic Materials?
Splattered blobs of lava that land as volcanic bombs.
Describe a composite cone volcano.
Very large in height and width. Cone shaped.
Intermediate to celtic lava.
Describe a cinder cone volcano.
Small with steep slopes, fragments of basaltic cinders and ash are found throughout the volcano.
How are calderas produced?
When huge amounts of pyroclastic debris and faces are released through ring fractures surrounding the summit, the crater produced by the pressure of these materials is called a caldera.
True or False: Magma’s viscosity is directly related to its silica content.
True: the more silica the magma has, the more viscous it is. Which also makes it more explosive.
Why and how is viscosity related to the magnitude of a volcanos eruption?
The more viscous the magma is, the greater its resistance to flow, therefore the greater the eruption.
