NCEA Level 1 Geography AS 1.1 "Extreme Natural Events" - how volcanic eruptions affect the natural environment

1. 11 Geography
Different types of Volcanic Landforms

2. There are many different types of volcanic landforms.
Often these are caused by the different types of
eruptions that we looked at previously.
So first… what were the main types of eruptions?
Ex_________________ Magma is ___________ because it contains a lot of ___
Eg…r________________________________
Ef_________________ Magma is ___________ because it doesn’t contain so
much _________ eg b__________________________
UNLESS the magma meets ______________________
Then it may cause a __________-________________
Ex________________ ← eruption

3. Two main categories of landforms
• Cone = a
hill, mound, mountain, dome, peak, cone etc – a
new or altered landform that sticks up out of the
ground
• Crater = a basin, hollow, depression in the ground
that will probably get filled up with freshwater
(eg a lake)
or saltwater

4. 3 Main types of volcanic cones
• Scoria Cone (or cinder cone)
• Shield Volcano
• Stratovolcano (or composite cone)

5. Scoria Cone
• Otherwise known as a cinder cone
• Sides are quite straight with steep slopes
• Large summit crater
• The lava and tephra are usually basalt
(or sometimes andesitic) which means it
is quite runny

6. Scoria Cone continued
• The eruption type is usually Strombolian which
means it has fire fountains

7. Strombolian Eruption

8. Scoria Cone continued
• A good example around Auckland is Maungawhau
(Mt Eden) – steep, straight sides, crater in centre

9. Shield Volcano
• Very gentle slopes; convex
upward
• Basalt lava flows - the lava
flows easily away from the vent
in large sheets, or follows
existing stream valleys
• Sometimes caves or tubes form
in the lava, other times large
columnar basalt formations

10. Shield Volcano continued
• The eruption type is known as hawaiian,
• producing lava flows known as aa or pahoehoe

12. Shield Volcano continued
• Rangitoto is a good example of this type of volcano
• Gentle slopes
• “Aa” lava flow
on Rangitoto

13. Stratovolcano or Composite Cone
• Gentle lower slopes, but steep upper slopes;
concave upward;
• small summit crater
• Highly variable lava types; alternating basaltic
to rhyolitic lava and tephra with an overall
andesitic composition.
• This means that the lava often has a lot of
trapped gas, so it is very sticky
• The cone is built up over a long period of time
by many eruptions of various types

14. Stratovolcano continued
• This eruption type is known
as Plinian or Vesuvian
• These eruptions can be
huge, long-lasting and
extremely dangerous

16. Stratovolcano continued
• When these volcanoes erupt they emit volcanic
products that also have major impacts on the
land and natural environment:
• Pyroclastic flows
• Lahars
• Ash showers
• In New Zealand volcanic activity has built up a
huge volcanic plateau (area of upraised land) in
the Central North Island.

17. Pyroclastic flows
• huge clouds of ash, rock and hot gas that sweep downhill at
incredible speed, flattening anything in their way

18. Lahars
• A flow of liquid mud down a mountain or valley
• NZ’s most famous is the Whangehu River
lahar, Christmas Eve 1953, causing the Tangiwai
Disaster

19. Ash showers
• Thick layers of gritty, acidic volcanic ash fall in a
thick blanket, choking the landscape

20. Craters
• A caldera forms when a huge
stratovolcano collapses in on
itself after a major eruption
sequence, creating a massive
crater
• Usually this fills with water to
form a lake
• Rotorua and Taupo both
formed in this way

21. Lake Taupo – a caldera

22. Maar
• A crater caused by a phreato-magmatic eruption
• This is when hot magma encounters groundwater
and explodes out of the ground
• Auckland has several examples, such as Lake
Pupuke, Tank Farm, Onepoto Basin, Panmure Basin
and Orakei Basin
• A maar is often surrounded by a tuff ring = a ring
around the edge of the crater made of layers of
ash, soil and scoria
• Maars usually fill up with freshwater or seawater

24. 3D map of Auckland volcanoes

25. A really useful website about volcanic eruptions
• http://www.squidoo.com/volcano-glossary