Post on 12-Jan-2016
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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
East
Pacific
Rise
Mid
Atlantic
Ridge
Mid Indian
Ridge
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
Often in the middle of a plate
Focus here on Hawaii & Oceania
Hawaiian Hotspot
Hawaii - also example of isostacy
Trail of the Hot Spot
Note change in direction 43 myr agoChange in direction 43 myr 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
Fringing Reef
Holand Island
Grand Cayman Is.
Tureia, Coral Atoll Oeno, Fringing Reef
Bora Bora Atoll
Climate: What would you expect?
Realm of the Intertropical Convergence Zone
Hadley Cell
Ascending
moist air
condenses
& rains
ITCZ
Equatorial & Tropical
Latitudes influenced by
ITCZ
0º
Descendingwarms & driesIn subtropics
Desertzone
Descendingair warms& dries insubtropics
Desert Zone
Trade winds Trade winds
Global CirculationPatterns
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 ofLatosol or Oxisol Soils
Laterization soil development
Oberlander & Muller, 1984
Soil Name
OxisolLatosol(synonyms indifferentclassifications)
Clay type(kaolinite)Not holdnutrients
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)
Mt Rotui, Moorea
Rarotonga, Cook Islands