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Uniformity & Catastrophe 2 (River & Valley Problem (Rivers cut out…
Uniformity & Catastrophe 2
Hutton's
Key Ideas
Episodes landscape renewal
cycles of uplift & denudation
Uplift related to internal heat
Laws act perpetually
ongoing forever
discovered 'deep time'
Valleys cut by rivers
flowing in them
Hutton's Cycle
1)
Land degraded
by river/ocean erosion
2) Horizontal strata form in oceans
heat & pressure builds under weight of sediments
3)
Magmas / melting sediment
causes expansion & uplift
forming new continents in old oceans
Hutton's Unconformity
Siccar Point
Vertical shales/greywackes ~ 420-440 Ma
Devonian sandstones ~350 - 400 Ma
overlain by
Field observation & theory helped understand u/c
River & Valley Problem
Rivers cut out valleys via erosion
until equilibrium reached (Hutton & Playfair)
How lakes form?
Erratic origins?
Some rivers very small ?
Before glaciation accepted, following problems posed:
Response to Hutton's Ideas
Growing acceptance denudation
erosion shaping landscape
gradual change contrasts catastrophism
Tho not as primary cause of valleys
View Landscape Shaping 19th Century
Scientific catastrophism
William Buckland
Initially supported Biblical Flood
- thought found evidence
Later supported
Louis Agassiz Theory of Glaciation
= slow catastrophe
Charles Lyell Uniformitarianism
Uniformitarianism
gradual change continuing indefinitely
Change always remained same - rate / state / process
Lyell's Principles
Uniformity of
Law
Laws constant over time & space
no 'supernatural' changes
Process
Explain events with known if possible
do not invent exotic processes to explain events
Rate
change is slow / steady / gradual
floods/equakes have local impact only
State
change is directionless
Earth has always looked like this
Reaction to Lyell's Principles
Polarisation of positions
valley origin
ordinary fluvial erosion?
multiple floods (vs one deluge) suggested by scientific catastrophists
ridiculing of catastrophic theories
proved limiting to some theorising
hindered glaciation/flood understanding for some time
Catastrophism Following Lyell's Principles
Some catastrophists remained
opposing uniformitarianism presented by Lyell
Ridiculing of catastrophist theories
hindered glaciation / flood understanding
Problems Remaining
Erratics
Diluvial deposits
Anomalous valleys - misfit streams
Present Debates
Magnitude - Frequency Relationships
of gemorphic events
which are more important -
infrequent high mag OR long t small mag change
Reasses significant rare, catastrophic events
on other planetary surfaces e.g. Mars
on Earth i.e. Spokane Missoula Flood