Waking the Giant Flashcards
Chapter 4, 5, 6, 7,
What is Isostasy?
This is the Earth’s crust response to the addition or removal of mass from the surface of the Earth.
When mass is added, the crust is pushed down.
When mass is removed, the crust rebounds.
What is glacial isostatic adjustment?
The way the Earth’s crust responds to the weight of a glacier.
At A, the crust is pushed down.
At B, next to the glacier, the crust is pushed up, forming a peripheral bulge.
What is the link between ice ages, the weight of ice and liquid water and earthquakes? Give an example.
The added weight of an ice sheet on the Earth’s crust will reduce earthquake activity. Ice will contain the rock.
The presence of a large body of water on the crust, such as a lake also represents a significant weight. However, earthquake activity is not inhibited, it may even increase beneath a lake. The weight of all this water forces it into the underlying bedrock where it can cause rocks to move and earthquakes to happen, because of increased water pressure in the pores.
A possible example of isostatic rebounds and earthquakes: New Madrid Earthquakes - 1811 1812-
During the last ice age, the laurention ice sheet covering most of North American pushed the crush beneath it down. Next to it, the crush rose upward in the form of a peripheral bulge.
When the glacier melted, the crust rebounded and the peripheral bulge collapsed. Perhaps the collapse of the bulge contributed to the New Madrid Earthquakes
Why are volcanoes so unstable?
Why are volcanoes so unstable?
A volcano is composed of layers of solidified lava and pyroclastic debris.
During and between eruptions there is heat and there is gas. There is also liquid water. Therefore inside a volcano there are many different chemical reactions that will weather the volcano. This big pile of loose weak rock is unstable. Volcanoes are prone to failure; they fall down.
When you add water:
Pore water increases
The contacts between rocks is lubricated, thereby reducing friction
Weight is added to the structure
All these things will increase the possibility that rocks will fall off the sides of the volcano: if more rock is removed then the likelihood of an eruption increases because there is less rock to contain the pressure.
What is the link between volcanic eruptions and sea water temperature?
Volcanos erupt when the rock surrounding the magma chambers cannot contain the pressure
The rock that makes up the volcano is weak and unstable
What makes this rock even more prone to failure is more water
Extra water on a volcano comes from the atmosphere in the form of rain or snow
Most water that eventually falls as rain or snow comes from evaporation of surface water in the oceans
Warmer sea water increases the rate of evaporation which increases precipitation
It appears then that warmer sea surface temperatures would coincide with more volcanic eruptions. However the link is not direct and the process (ocean circulation and volcanic eruptions are so complex and so different that any link is tenuous at best)
Describe the Zanclean Flood
Mediterranean sea and straights of Gibraltor. (5.3myrs ago) pg 208-209.
What affects will sea level rise have on the earthquake hazard here on the west coast of British Columbia?
The earthquake hazard is related to an Oceanic VS Continental convergent plate margin - The largest earthquakes occur at the coast or further off shore. As sea level rises, more weight will be added to the coast. This may effect the stress that continues to build up at this plate margin. As stress changes more, larger earthquakes may occur. It may also be that fewer earthquakes may happen.
A lot has been made of climate change and how it will impact the Earth. If a worse possible scenario takes place and the Earth’s atmosphere warms significantly how might this affect the frequency and magnitude of potentially catastrophic geological events such as volcanoes, earthquakes and landslides?
If climate changes there will be significant increases in sea level meaning there will be more weight bearing down on coastal areas. Climate change also means there will be more extreme weather events such as storms. This means there will be more, sudden shifts of water in coastal areas. Both scenarios suggest an increase in the frequency, size and duration of events where large masses of water are moved on the earth’s surface. Shifting weights (water) of this magnitude can change the behavior of volcanoes, earthquakes and landslides. This change could be an increase in frequency and magnitude.
