Transcript Template # 2

Physical Geography Tidbits:
Oceania
Formation of Oceania Islands
Reason for
Movement
Excess heat from
radioactive decay
creates liquid
outer core (and
magnetic field),
and forces mantle
to have
convection
Exactly
how
mantle
moves?
ASU view
3 TYPES OF PLATE INTERACTION
Stream Systems on
Dynamic Earth
New Zealand - 2 of the 3
Mid
Atlantic
Ridge
East
Pacific
Mid Indian
Ridge
Rise
Millions of years before present
Island Arcs from Ocean-Ocean
Convergence
Trench
Island arc
Older colder
ocean plate
subducts
Convergence &
Tsunami
Effects Of Plate Locking
EQ (or landslide or volcanic
eruption ) Movement Generates the
Wave that travels about 500 mph
Animated gif
Mega-Quake
Set off 2004
Tsunami &
will happen
again
Energy ripple
Sri Lanka
Sumatra
Uplift
Indonesia
Indonesia
Has Happened, Will Happen Again
Hilo, 1960
Chile EQ generated
Tsunami that destroyed
Hilo in 1960
Hot Spots
Focus here on Hawaii & Oceania
Often in the middle of a plate
Hawaiian Hotspot
Hawaii - also example of
isostacy
Trail of the Hot Spot
Note
changeinindirection
direction4343myr
myrago
Change
ago
Are plumes real?
Alternative
Hypothesis
After Formed … Sink
This NOAA animation shows the dynamic process of how a coral atoll forms. Corals (represented in tan and purple)
begin to settle and grow around an oceanic island forming a fringing reef. It can take as long as 10,000 years for a
fringing reef to form. Over the next 100,000 years, if conditions are favorable, the reef will continue to expand. As
the reef expands, the interior island usually begins to subside and the fringing reef turns into a barrier reef. When
the island completely subsides beneath the water leaving a ring of growing coral with an open lagoon in its center,
it is called an atoll. The process of atoll formation may take as long as 30,000,000 years to occur.
http://www.oceanservice.noaa.gov/education/kits/corals/media/supp_coral04a.html
Grand Cayman Is.
Fringing
Reef
Holand Island
Tureia, Coral Atoll
Oeno, Fringing Reef
Bora Bora Atoll
Climate: What would you expect?
Realm of the Intertropical
Convergence Zone
Hadley Cell
Ascending
Descending
warms & dries
In subtropics
moist air
condenses
Trade winds
& rains
Trade winds
Descending
air warms
& dries in
subtropics
ITCZ
Equatorial & Tropical
Desert
zone
Latitudes influenced by
ITCZ
Desert Zone
Global Circulation
Patterns
Hadley
Cell
Little Seasonal Change in Temp
Soils of the Tropics
Soils form over tens of thousands of years
Gives you a
“map” of
the
“average”
location of
rainforests
& savanna
Synonym: Oxisol Soils
Process of
Latosol or Oxisol Soils
Laterization soil development
Soil Name
Oxisol
Latosol
(synonyms in
different
classifications)
Clay type
(kaolinite)
Not hold
nutrients
Oberlander & Muller, 1984
Oxisol Profiles
• Little organic
matter
• Red from
iron oxides
• Loose &
friable
texture
Paradox: Poor soils because few
nutrients, yet great rainforests
Why? Natural nutrient recycling
With
Deforestation
• organic matter leached
• nutrients lost
• Gradual loss of fertility
With deforestation
• soil structure hardened by desiccation and
compaction into laterite
• Can make “laterite” by drying out the soil
Deforestation has always occurred:
traditional swidden (slash and burn)
agriculture – burn to release
nutrients and move to another plot
Feral relief
Steep landscapes
made by landsliding
from intense rains
in places like Hawaii
Andes where a lot
of relief exists
Steep slopes made possible by
vegetation holding soil to steep faces
Intense rains saturates slopes and
landslides rush down slopes
Flat valleys eroded by torrential
floods
Landslides strip
trees
Net effect is relief gone wild (feral)
Kauai
(GoogleEarth)
Rarotonga,
Cook Islands
Mt Rotui, Moorea