Earth History GEOL 2110

Lecture 2Scales of Time and Change

Major Concepts

• Geological events cover huge amounts of time that are hard to grasp in the span of human life

• We tend to focus on dramatic, short-lived geologic events that we witness and are unaware of subtle, but geologically important events

• Very often, short dramatic events are just parts of long-lived processes (e.g. mountain building, sea-level change)

• Rates of geologic change can be linear, non-linear, periodic or episodic

Dramatic, Short-lived EventsVolcanic Eruptions

Krakatoa , 1883• left a 3000m deep crater• ash dispersed 2000km away• heard 5000km away• 40m high tsunamis• lowered global T for 2yrs

Dramatic, Short-lived EventsVolcanic Eruptions

Santorini/Thera – 3,600ybp• 3-4x bigger than Krakatoa• Minoan civilization on Crete to devastated by

earthquakes and tsumamis• Inspired the myth of the lost city of Atlantis

Dramatic, Short-lived EventsVolcanic Eruptions

Mt. St. HelensMay 18, 1980

Summit -9,677’

Crater Base -4,700’

Dramatic, Short-lived EventsVolcanic Eruptions

Mt. Mazama Eruption6,500 ybp

Great Time Markers!

Dramatic, Short-lived EventsVolcanic Eruptions

Heimaey, Iceland1983

1326 Aftershocks

Dramatic, Short-lived EventsEarthquakes

1326 Aftershocks

Dramatic, Short-lived EventsEarthquakes

Anchorage, Alaska1964

9.3, 131 Dead

Dramatic, Short-lived EventsEarthquakes

San Francisco, California - 19067.8

200,000 homeless and >3,000 dead3 days of fires destroys 70% of city

Dramatic, Short-lived EventsTsunamis

Banda Aceh, Sumatra

9.15

>200,000 killed

Dramatic, Short-lived EventsIn Real Time

Earthquakeshttp://earthquake.usgs.gov/earthquakes/map/

Volcanoeshttp://www.volcano.si.edu/reports/usgs/

Subtle Geologic EventsClimate Change

The Sahara10,000 Years ago – Temperate, Humid, Verdant

Subtle Geologic EventsClimate Change

Subtle Geologic EventsGlaciers and Sea Level

Subtle Geologic EventsGlaciers and Sea Level

Cosquer Cave, France37 m deep entrance

Horse - 18,500 years old

Ibex

Subtle Geologic EventsGlaciers and Sea Level

Greenland's Jakobshavn Glacier

Subtle Geologic EventsGlaciers and Sea Level

Projected sea level rise (5 m) for NorthwesternEurope. Population at risk in the inundation area is calculated at over 21.7 million people(Rowley et al. 2007)

Current climate models predict that sea levels will rise 25-60 cm over the next century

Melting 10% of Greenland and Antarctic Ice Sheets would produce ~5 m rise in sea level

Subtle Geologic EventsGlacial Retreat & Crustal Rebound

Subtle Geologic EventsGlacial Retreat and Crustal Rebound

Subtle Geologic EventsGlacial Retreat and Crustal Rebound

Rates of Geological Processes

Linear Change(rare in nature) Non-Linear Change

(more common)

Rates of Geological ProcessesPeriodic to Episodic Change

Most Common toGeological Processes

Evolution of Ideas about Rates of Geological Processes

Pre-1700

Late 1700’s- Mid-1800’s

Mid-1800’s –Late 1900’s

Present-day

Biblical Creation <6000yDeluge central to geological interpretation

Catastrophism

UniformitarianismPuNctuAteD eQuiLibRiuM

Next Lecture

Development of Geological Concepts

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