Week 6 Flashcards
1
Q
What Causes an Eruption?
A
- Magma is less dense then crust, rises to top
- Reaches the surface, erupts if the pressure of the volatiles is greater than the weight of the rock covering the volcanic neck, known as the cap
2
Q
An eruption will be explosive if:
A
- The magma is viscous (indicating high Si-content)
- The magma is saturated is exsolved volatiles
- The cap suddenly ruptures/breaks
3
Q
Volcanoes Case Study: The Cascade Range
A
- Host to more than a dozen subduction zone volcanoes
- Mount St Helen’s erupted in 1980, resulting in one of the most spectacular natural disasters to date
4
Q
The Cascade Range Dates
A
- Mar 21 1980, M4.2 earthquake was the first sign magma was moving up the volcanic neck
- April, 1980 – A magma dome/bulge was forming, growing at a rate of 1m/day
- May 12, 1980 – The magma dome was now ~150m tall; evacuation orders issued
- May 18, 1980, M5.1 earthquake caused a huge section of the north side of the volcano to calve along a series of normal faults
- Overall, a volume of 1km3 of volcanic material was ejected during this event, with ashfall spreading as far as Minnesota (more than 2500km away!)
5
Q
Mount Mazama is one of the most fantastic volcanoes in the USA; known more commonly as ‘Crater Lake’
A
- So violent and destructive, blew an entire 1000m off its top
- 8km wide and 600m deep
- Crater Lake contains many cinder cones and lava flows escape into the lake, polluting it with volcanic gases
6
Q
Plinian Eruption
A
An eruption throwing pyroclastic material high, vertically into the atmosphere.
7
Q
Peléan Eruption
A
An eruption throwing pyroclastic material laterally, often resulting in nuée ardente.
8
Q
Volcanoes Case Study: Krakatau
A
- 3 cones on three islands
- The largest, Rakata, sat as a steep-sided mountain in the middle of the Sunda Strait, an important shipping route in the region
- 535AD, Krakatau erupted ash that blocked the sunlight and lowered the global climate by 1-2ºC
9
Q
Krakatau 1883 Lead up
A
- May, small eruptions, steam from top
- July, heavier eruptions and steam
- steam from water entering cracks
- August 26, explosions which allowed a lot of water to enter
- Created pressurized steam
10
Q
Krakatau 1883 Eruption
A
- 4 huge explosions 13X Hiroshima
- Geographically, +813M to -300M elevation
- Loudest sound in historical time, heard 3,100km away in Perth, Australia!
- Within 2 weeks, ash and dust had spread to everywhere on Earth; global temperatures dropped 0.5ºC, and were affected for the next five years
- Tsunami in Sunda Strait, 37M waves drowning 36,417
11
Q
Volcanoes Case Study: Mount Vesuvius
A
- Naples Italy
- Prior to 62AD Romans did not know earthquakes
- 79AD black smoke above volcano
- Deadly Lahar from eruptions
- Ash travelled 9km to Pompeii and covered it, deadly
12
Q
Volcanoes Case Study: Hawaii
A
- Mantle plume from intraplate hotspot
- crust moving with static plume creating extinct volcano chain
13
Q
Mauna Loa
A
- Largest volcano on Earth, and is so massive it is flexing down the oceanic crust beneath (Hawaii)
- Gentle ~3-5º slope, meaning lava can spill out non-explosively
14
Q
Mount Kilauea
A
- Violent neighbor to Mauna Loa
- Dec 2020, 9km high pyroclastic material
- 216M lava lake formed, crusted over May 2021
15
Q
Volcanoes Case Study: Yellowstone
A
- When a hotspot pierces continental crust, dangerous volcanoes form because chemical alteration Resurgent Calderas
- 3 big eruptions
