Lecture 4 Flashcards
1
Q
Primary factors that determine eruption style ?
A
- Composition of magma
- Temp. of magma
- Amount of dissolved gasses
2
Q
Viscosity ?
A
- Directly related to its silica content
- Felsic lavas form short, thick flows.
- Mafic lavas tend to be fluid and travel long distances
3
Q
Importance of dissolved gases ?
A
- Increase fluidity of magma
- Provide force to propel magma from vent/conduit
- Migrate upward contributing to summit inflation
- High viscous magmas expel jets of hot hashladen gases evolving into eruption columns
4
Q
Lava flows ?
A
Mafic lavas are much mmore fluid and flow easily
5
Q
Type of mafic flows ?
A
- Pahoehoe flows
- Aa flows
- Pillows lavas
6
Q
Lava tubes ?
A
Cave like tunnels below hardened lava that allow molten lava to continue flowing
7
Q
Gases ?
A
- 1 to 6% of magma by weight
- Held in magma by confining pressure
- Mainly water vapour and carbon dioxide (also nitrogen and sulphur dioxide)
- Volcanoes are a natural source of air pollution
8
Q
Pyroclastic materials ?
A
- Ejected fragments from europtions taht range in size from dust to pieces several tonnes in weight.
- Hot ash falls and glassy shards fuse to form welded tuff
9
Q
Type of pyroclastic debris by size
A
- Ash and dust (Fine, glassy fragments)
- Lapili or cinders (2-64 mm diameter)
- Blocks (Ejected as hardened lava)
- Bombs (Ejected as hot lava)
10
Q
Type of pyroclastic debris by composition and texture
A
- Scoria (Vesicluar ejecta from mafic magma)
- Pumice (Vesicular ejecta from silica-rich magma)
11
Q
Nuee ardente : A deadly pyroclastic flow ?
A
- Can be called glowing avalanches
- Fiery pyroclastic flows made of hot gases infused with ash and others debris
- Can reach speed of 100km/h
12
Q
Lahar ?
A
Mudflow off steep sided volcanoes
13
Q
Triggers of lahar ?
A
- Large volume of ice and snow melt during an eruption
- Heavy rainfall saturates weathered volcanic deposits
