ERTH308 Movie Notes Week 3 - Julia Boring
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Geology
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Apr 3, 2024
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Questions on Where Terranes Collide: The Geology of Western Canada
1. What were the origins of the rocks composing the Intramontane Superterrane?
The Stikinia and Quesnellia terranes consisted of volcanic chains and reefs that had been forming for millions of years in the southern parts of the Pacific Ocean. The Slide Mountain and Cache Creek terranes consisted of ancient sea floor that formed at sea floor spreading ridges.
2. How many terranes were amalgamated (joined together) into the Intramontane Superterrane?
Four. The Stikinia, Quesnellia, Slide Mountain, and Cache Creek.
3. What is a melange rock, and where do they typically originate?
Melange rock is different kinds of rock all mixed together. It describes the disruption that
happens at the seafloor at subduction zones, which is where they typically originate. 4. What happened to the rocks forming the edge of the continent as they collided with the continent?
As this collision happened, the intense heat and pressure resulted in the rocks at the edges to become compressed, deformed, and melted. It made a big welt of traumatized rock called the Omineca Belt. Just a Couple Questions on Regional Alaskan Tectonics
1. The distance between the trench (marking the boundary between the subducting oceanic plate and the overriding continental plate) and the volcanic arc (produced by partial melting of the mantle wedge above the descending slab) varies from one end of the Aleutian volcanic arc to the other. What determines this distance?
The distance is determined by the subduction angle of the plates. 2. In the 2002 M 7.9 Denali Fault Earthquake, how much slip (displacement) occurred along the fault, and how far away were the effects felt?
It produced 8 meters of right lateral displacement, and created a total rupture length of 340 kilometers. The effects were felt up to 3600 kilometers away and affected geotherm
activity in Wyoming. In the Path of a Killer Volcano
Questions:
1. In the predictions of the 1980 Mount St Helens eruption, what did volcanologists get right, and what did they get wrong?
They were correct about the time, but incorrect about the size and lateral direction of the blast.
2. Who first noticed the renewed activity of the Philippine volcano?
A nun first noticed the renewed activity.
3. What are the three possible explanations for earthquakes beneath a volcano?
Magma rising from the earth's crust, the mountain was letting off excess steam, or tectonic stresses from shifting in the earth's crust. 4. On the flight to the Philippines, USGS volcanologists passed over Katmai Volcano, Alaska, which
erupted in 1912. Why was this relevant to Mt Pinatubo?
While looking down on Katmai, they took note of the ash and pyroclastic flows. When they looked at the Pinatubo they then noticed the similarities between the two. 5. What did carbon dating of incinerated trees reveal about the eruptive history of Pinatubo?
That the mountain has only erupted 4 or 5 times in the last 2000 years. Infrequent eruptions almost always mean violent eruptions. 6. IMPORTANT: What are three primary methods of monitoring a volcano to predict whether or not it will erupt??
Seismic monitoring, gas emission monitoring, and ground measurements. 7. Which of these methods tells you if magma is moving beneath the volcano?
Seismic 8. Which method tells you if the volcano is plugged and may be nearing eruption?
Ground deformation
9. What is a pyroclastic flow
? What is a typical temperature and speed of a pyroclastic flow?
They are hot avalanches of ash, rock, and gas. They can reach 100MPH and around 200 degrees F.
10. What is a lahar
?
It is a hot mud flow
11. Geological interpretations have consequences. The film refers to two other significant failures to accurately predict volcanic activity. What were they, and how do they illustrate the issues facing volcanologists in this situation?
In 1986, one day after scientists decided it posed no immediate threat, a volcano in Columbia erupted and sent a hot mud flow down killing 2200 people. The other significant failure talked about was in 1982 when scientists issued warnings affecting Mammoth Lakes, California. When nothing happened townspeople reacted with anger that persisted for years afterwards. These situations explain the pressure volcanologists face in order to be correct and precise in every prediction. 12. What did the spine or dome of fresh magma indicate?
It indicated an explosive kind of magma was underneath. It showed the ground underneath was unhappy and was a sign of a possible eruption coming soon.
13. How many people died in the actual eruption? How many were successfully evacuated?
14 thousand were successfully evacuated. Under 500 people died in the actual eruption. 14. How does this eruption compare in volume to St Helens in 1980?
It was about 10 times the size of the St Helens eruption
15. How long after the evacuation did the volcano erupt?
48 hours later
16. How much time passed between the first big eruption and the climactic eruption of June 15? And how long did these eruptions continue?
The first notable eruption happened on April 2, and the biggest eruption took place on June 15. The smaller eruptions lasted for weeks after the big eruption 17. Ash from the eruption circled the globe within weeks. What were the effects on global climate, and for how many years?
The widespread ash had a cooling effect on the globe. It also created a big aerosol cloud due to the sulfur dioxide in the ash and volcanic gasses. These impacts were most impactful in the couple years following the eruption.
18. Would you consider this a successful prediction of a volcanic eruption? Why or why not?
Yes, I would consider it to be a successful prediction of a volcanic eruption. The scientists monitored the volcano closely and based on their findings would update alert levels and inform authorities. They implemented an evacuation that saved many people’s lives, and made the call at just the right time.
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