Download 9.2 – Sea Floor Spreading

Mrs. Guzman
2/28/11
 Sonar
used to map out the majority of
features
• Deep Trenches
• Mid-Ocean Ridges
• Rift Valley
• Mountains
• Volcanoes
 Made
of Igneous Rocks covered with
sediment (not quite considered “rock” yet)
 More sediment the further away from
ridges
 This means that _____________________
 New
floor at mid-ocean ridges due to
eruptions. Moves outwards
 Old floor sinks again at subduction
zones at edges of continents in trenches
Magnetic Pole Reversal
The Earth's magnetic
poles moveup to 50 miles
(80 km) per day. (average
of 25 miles per year)
•In the last 150 years, the
pole has wandered a total
of about 685 miles
•The last time the poles
switched was 780,000
years ago, and it's
happened about 400
times in 330 million years
Source: www.howstuffworks.com
 Earth’s
magnetic field sometimes
switches polarity
 Igneous rocks usually contains
magnetite, which is magnetic. As it cools,
its particles align to the N/S poles and
remains until melted again.
 Shallow
earthquakes around a trench
 Intermediate earthquakes as oceanic
lithosphere is pulled under continental.
Melting also occurs and we see
volcanoes directly above on surface
 Deep earthquakes furthest from trench
and further in from volcanoes
 Age = Youngest rock is closest to the
ridge and oldest is closest to trench
 Also
on Dynamic Planet USGS Map