Volcanology questions
Question #1 (2/22)

Q1. Contrast the differences between basaltic versus rhyolitic magma in terms of:

answer #1

Question #2 (2/24)

Q2. What changes on temperature, pressure, and water content will cause a hot rock to melt?
(assume the rock is just below its' melting curve or 'solidus' in a T-P diagram)

answer #2

Question #3 (2/26)

Q3. Identify the probable styles of eruption for magmas with the following characteristics:

  1. low silica (basalt) and low water content
  2. intermediate-to-high silica and high water content
  3. high silica (rhyolite) and low water content

Possible answers: Icelandic, Hawaiian, Strombolian, Vulcanian, Plinian, Peleean types, or 'effusive lava', 'explosive pyroclastic', 'dome-building', etc. (Use as many answers as you think fit.)

answer #3

Question #4 (3/1)

Q4. For the following types of plate boundaries, what are the predominant types of volcanoes and what significant hazards do they pose to humankind?

  1. divergent margins [e.g., mid-oceanic spreading centers]
  2. convergent margins [e.g., Cascades, Aleutians, Japan]
  3. transform margins [e.g., San Andreas or Dead Sea fault zones]

List any other geologic settings for which there may be significant volcanic hazards - give an example.

answer #4

Question #5 (3/3)

Q5. In the United States there are numerous active or dormant volcanoes. Select one active area/volcano that you believe poses a significant hazard, and briefly describe the most serious impacts it may have on society in the future.

(How should we, or the government, prepare for this eventuality?)

Climate Change questions
Question #6 (3/15)

Q6. What is the difference between 'weather' and 'climate'?

answer #6

Question #7 (3/17)

Q7. What is the 'Greenhouse effect'? Explain in terms of atmospheric composition.

answer #7



A1. Basaltic magmas have higher temperature (> ~1150°C), and lower SiO2 (< ~52%) and viscosity (very fluid) than rhyolites (typically <800-900°C, >68% SiO2, and very 'pasty' or inviscid).

These properties, and the added influence of water, control the styles of eruption of these magma types.

A2. Any of the following changes, if sufficient in degree, will cause the rock to begin melting:

A3. Examples:

  1. Icelandic or Hawaiian 'effusive lava'
  2. Strombolian, Vulcanian, Plinian, or Peleean 'explosive pyroclastic', depending on specific magma composition, extrusion rate, etc.
  3. 'dome-building' primarily, or viscous blocky flows (for high extrusion rates)

A4. Volcanism associated with tectonic plate margins:

  1. Divergent: Rift-style sheet flows and numerous small basaltic volcanoes; these are rarely hazardous to people because they are so remote.
  2. Convergent: Large stratovolcanoes and associated magmatism; these are most threatening to people because they commonly erupt explosively or produce lahars, both of which can affect large geographic areas, and even have global atmospheric effects. Unfortunately, these also frequently occur near highly populated areas.
  3. Transform: What little volcanism occurs in these settings is usually small in volume, not very explosive, and thus has relatively little impact on people. [The movie Volcano rather overstates the volcano hazard threat in such areas.]


A6. 'Weather' describes the short-term variations in atmospheric conditions - on time scales ranging from hourly, daily, or even seasonal.

'Climate' refers to these variations on longer time scales - decades, centuries, or millenia.

A7. The 'greenhouse effect' is a warming of the Earth due to trapping of solar energy reflected from Earth's surface by so-called 'greenhouse gases in the atmosphere. These gases include water vapor, methane, and carbon dioxide, all of which occur in very small amounts; because of their strong absorption properties they have a significant effect on energy retention, thereby contributing to global warming.