FORCES WITHIN EARTH

PlateTectonicsEarthquakes

&Igneous Activities

California Standardsfor Earth Science

Dynamic Earth Processes 3. Plate tectonics operating over geologic time has changed the

patterns of land, sea, and mountains on Earth’s surface. As the basis for understanding this concept: a. Students know features of the ocean floor (magnetic patterns, age, and sea-floor topography) provide evidence of plate tectonics. b. Students know the principal structures that form at the three different kinds of plate boundaries. c. Students know how to explain the properties of rocks based on the physical and chemical conditions in which they formed, including plate tectonic processes. d. Students know why and how earthquakes occur and the scales used to measure their intensity and magnitude.

e. Students know there are two kinds of volcanoes: one kind with violent eruptions producing steep slopes and the other kind with voluminous lava flows producing gentle slopes.

f.* Students know the explanation for the location and properties of volcanoes that are due to hot spots and the explanation for those that are due to subduction

Plate Tectonic Theory

CONTINENTAL DRIFT HYPOTHESIS

EVENTUALLY LED TO: PLATE TECTONIC THEORY EVIDENCE INCLUDES:• SEAFLOOR TOPOGRAPHY• IGNEOUS ACTIVITY• EARTHQUAKES• PALEOMAGNETISM

PLATE TECTONICS

EARTH’S LITHOSPHERE (CRUST AND UPPER MANTLE) IS DIVIDED INTO SEVEN MAJOR PLATES AND

MANY SMALL ONES

VERY FEW SCIENTISTS AGREED WITH WEGENER UNTIL:

Alfred Wegener first proposed his hypothesis in 1915 that all of the continents were once joined together – called Pangea.

His only problem was explaining the mechanism for the movement of continents.

New technology came along to map the deep seafloor.

Better technology was available to study earthquake patterns.

Drill and take samples from the seafloor.

New theory emerges in 1960’s.

Plate Boundaries

When Plates interact (come together), they do one of three things:• Push together – Converging Plate Boundary• Pull apart – Diverging Plate Boundary• Slide by each other – Transform Fault Boundary (our San Andreas Fault)

Earthquakes

• Vibration of Earth due to a rapid release of stored energy.• Usually caused by slippage where two plates meet.• The 1906 San Francisco quake was studied carefully and led to current hypothesis about cause of earthquakes.• Much of what we know about composition and structure of earth is from studying earthquakes.• Scientists observe patterns of shock waves from earthquakes to determine location of quake and characteristics of Earth’s interior.

Tsunamis• Earthquakes that move or displace part of seafloor starts the wave in motion.• Waves move energy – not water.• Moving across the ocean, they are very low and long until they reach land.• These waves can travel at 500 – 950 km/hr.• Often called tidal waves but they are not caused by tides or ocean currents.• They can cross entire oceans before they strike land.

Volcanoes

Volcanoes and igneous (molten rock) activity starts with movement of tectonic plates deep in the lithosphere.

Factors that determine whether a volcano erupts quietly or violently and the resulting shape after the eruption depends on:• composition of magma• temperature of the magma• how much dissolved gas is in the magma.

Intrusive Igneous ActivityPLUTONS ARE IGNEOUS STRUCTURES THAT COOL AND HARDEN BENEATH THE SURFACE. TECTONIC MOTION AND WEATHERING EXPOSE THESE STRUCTURES OVER TIME. THE SIERRA NEVADA MOUNTAINS RANGE IS A VERY LARGE EXAMPLE OF THIS PROCESS.

GASSING AT THE SURFACE INDICATES MAGMA IS FORMING

NEAR THE SURFACE AND CREATES HOT SPRINGS