1. Geology Notes
Part 8 1

2. What causes earthquakes?
When plates slide past each other, collide, or move apart . 2

3. What is the elastic rebound theory?
It explains how rocks spring back into their original shape after they have been deformed by seismic forces 3

4. What is a seismograph?
Instruments that record the vibrations of the Earth during an earthquake 4

5. How are earthquakes measured?
The Richter scale of magnitude is a scale used that measures the amplitude (height) of seismic waves 5

6. Richter Scale 1.0 = 32 x energy 2.0 =1024 x 3.0 = 32,000 x
4.0 = 1,000,000
5.0 = 32,000,000
6.0 = 1,000,000,000
7.0 = 32,000,000,000
8.0 = 1,000,000,000,000
9.0 = 32 x 1013 ( ) 6

7. What is the epicenter? What is the focus?
The position on the Earth’s surface directly above the focus of an earthquake
What is the focus?
The point at which stress breaks the friction lock between two plates of the Earth’s crust 7

8. What is the relationship between plate tectonics and earthquakes?
Most earthquakes occur along plate boundaries.
Most large earthquakes occur along convergent plate boundaries.
Earthquakes occur deeper and deeper as one plate is being subducted under another plate. 8

9. What impact do earthquakes have on humans?
Earthquakes cause buildings and other structures to collapse which causes the most injury and death.
Other dangers include landslides, fires, explosions from broken gas lines, and floods from collapsing dams. 9

10. Where would you be most likely to feel a minor earthquake?
Someone on the top floors of a tall building.
Look at the distance the top of the building travels 10

11. Geology Notes
Part 9 11

12. What is a volcano?
A vent or fissure in the Earth’s surface through which magma and gases are expelled 12

13. What is the difference between lava and magma?
lava is the molten rock or magma that has reached the surface
Lava
Magma 13

14. Where do volcanoes generally occur?
They generally occur along plate boundaries when plates collide or move apart 14

15. What are the two different types of volcanic eruption?
nonexplosive or quiet eruptions produce calm flows of lava
explosive eruptions are rare and rapidly erupt ash and rock into the atmosphere 15

16. What are the different types of lava?
Aa lava is thin and forms brittle jagged crust as it cools
Pahoehoe lava flows slowly and forms a glassy wrinkled crust 16

17. What are the different types of lava?
Pahoehoe
Pahoehoe Aa Aa Aa 17

18. Pyroclastic Materials18

19. What is a shield volcano and how do they form?
formed by quiet eruptions
thin lava that spreads out over a wide area
sides are not steep 19

20. Photograph of the Hawaiian volcano, Mauna Kea, with a light dusting of snow, seen from Kohala above Kamuela. Photograph by Eric Guinther provided to Wikipedia under GNU. 20

21. Belknap Shield Volcano, Oregon.21

22. What is a cinder cone volcano and how do they form?
Formed by moderatly explosive eruptions
the pyroclastic material forms steep sides 22

23. Tavurvur, Rabaul Caldera, Papua New Guinea
Tavurvur, Rabaul Caldera, Papua New Guinea. A small explosion from Tavurvur sends an eruption column into the sky a few weeks after it began erupting on September 19, Lava erupted from the cone in October 1996 and flowed through the breach in the crater (left center). 23

24. Mount Veniaminof, Alaska
Mount Veniaminof, Alaska. Steam rises from the cinder cone within the caldera of Mount Veniaminof in the final stages of an eruption in Lava flows that spilled down the side of the cone (dark areas) melted a pit in the summit ice cap about 2.3 x 1 km in dimension. 24

25. What is a composite volcano and how do they form?
Form from explosive eruptions followed by slower flow of lava
forms alternating layers of pyroclastic material and lava
Also known as a stratovolcano 25

26. Mount St Helens
1980 26

27. Snow-covered Kanaga Volcano in Alaska erupts a small column of tephra, gas, and steam. Kanaga is a stratovolcano. 27

28. What is a hot spot?
A volcanically active area far from a plate boundary 28

29. How can hot spots be used to determine the motion of tectonic plate?
Using the distance of volcanoes (such as the Hawaiian Islands) and their age, the direction and rate of plate movement can be determined. Distance ÷ Time 29

30. Current Eruption
Thursday, January 13, Mount Etna, Italy 30

31. How can volcanoes change the atmosphere, hydrosphere, and other Earth systems.
The lava, gas, and ash that erupt into the atmosphere can remain in the atmosphere and be dispersed around the world by global wind currents.
The sulfur dioxide combines with water vapor to form sulfuric acid, which reflects the sun’s energy back into space. This can cause global temperatures to decrease.
Also the acid rain has a negative impact on vegetation around the world
Effects can last for a couple of years to over 100 years. 31

32. How can volcanoes be used to determine plate boundaries?
Composite volcanoes usually form in straight lines along convergent plate boundaries as one plate is being subducted under another.
Convergent Boundaries 32

33. Geology Notes
Miscellaneous 33

34. What is the affect of gravity on tectonic plates?
Gravity is stronger with any tectonic plate that is more dense and older, so it will go beneath the less dense and newer plate. 34

35. What hazards are associated with destructive earthquakes and volcanoes?
Earthquakes – tsunamis, buildings with top floors being damaged, and fires
Volcanoes – lava flows destroy area around it, vegetation destroyed, pyroclastic material flying through the air 35

36. How did Earth form?
Earth formed from a cloud of dust and gas called a nebula.
When gravitational forces worked to pull the objects together the Earth was formed. 36

37. How did Earth’s early atmosphere form?
Earth’s beginning atmosphere formed from volcanic eruptions causing gases to come up and out from the mantle. 37

38. How did Earth’s oceans form?
Earth’s oceans formed from volcanic eruptions. Water vapor was one of the gases given off by the eruption and once it cooled and condensed, rain fell to Earth’s surface. 38