Photo interpretation / research
Materials ejected by volcanic eruptions can
be of considerable size. The Mt Gambier eruptions illustrate this.
Large fragments ripped from surrounding rock during the explosion are called volcanic
bombs. While they cannot travel as far as ash, they can form a
significant portion of the deposits near the vent. They often disrupted
the orderly deposition of ash layers with their impacts.
A.1 The bomb shown in Photo A is
dark, fine-grained, with gas holes. It is believed to have originated as
part of a volcanic layer that formed in a gentle lava eruption. What
rock is it? |
Air fall deposits
Photo 1: Air-fall deposits around Blue Lake crater rim
A. Volcanic bomb in bed of ash
B. Beds of ash of differing hardness
C. Lakeside carpark |
A.2 Shown are large white fragments within an ash layer
(Photo B). They come from the thick Tertiary layer upon which the
volcanic products lie. What rock are they?
A.3 In places the ash has hardened into rock (Photo C).
This rock may be called what? What factors contribute to volcanic ash
hardening into rock? |
Photo interpretation / research
Study the profile of the Blue Lake crater (right).
B.1 Three rock types are shown. List them in order from
oldest to youngest. Explain how you know this.
B.2 Classify these three rocks as igneous, sedimentary,
metamorphic. |
Photo 2: Blue Lake crater profile
|
Research
C.1 Volcanic
air-fall materials can be classified by particle size, ranging
from very coarse to very fine. What are these particle size groupings
and the name given to ash-fall deposits of each particular size?
C.2 Air-fall materials may fall onto, and sink into, lakes.
What is the name given to this kind of deposit? How does this type of
deposit differ from the more common type that fell onto land?
Research
D.1 Can you find out what happens to the water colour of the
famous Blue Lake during the course of a year? What do you think is the
most plausible explanation for this?
D.2 As the city of Mt Gambier draws its water supply from
the Blue Lake it is essential that potential pollution sources be
identified and carefully controlled. The lake level is mostly maintained
from groundwater supplies. What might be some potential sources of water
pollution in this type of water supply?
D.3 The Murray River is the water source for much of South
Australia; how do you think the quality of water from the Murray River
and Blue Lake compare?
|
Research
The
eruption at Mt Gambier was violent; ash was produced as materials were
blasted into small fragments through dramatic explosions. Fine ash can
travel considerable distances and can cause much harm. In historic times
there have been many violent and destructive ash eruptions around the
world.
E.1
Name some of the great ash eruptions of recent (or historic) times, and
list some aspects of the destruction that followed. You may wish to
present a group report in written or oral form to the class on the
causes and features of this event.
|
Research
- Internet
Study the
Mt Gambier Info Site
and the Web Site: Kinds
of Volcanoes - by Allen Glazner
F.1
According to the 'Kinds of Volcanoes' Web Site, what type of volcano is
the Mt Gambier complex?
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