GEOSC 10: Geology of the National Parks Plate Tectonics III: Making Mountains, Obduction, & Tsunamis Presented by Dr. Sridhar Anandakrishnan The Pennsylvania State University

GEOSC 10 - Geology of the National Parks Go Dog Go PJ Eastman, 1961

GEOSC 10 - Geology of the National Parks Appalachians

GEOSC 10 - Geology of the National Parks Sideling Hill, West VA

GEOSC 10 - Geology of the National Parks Review Tectonics is driven by heat. The plates (8 major ones, few small ones) move on the surface of the Earth. Oceanic plates are basaltic. ‣ Initially hot and buoyant... later cool and sink Continental plates are silica-rich, low-density, and buoyant.

GEOSC 10 - Geology of the National Parks Review (2) When cold ocean plates collide with continental plates, they “dive under” the continents. Subduction leads to ‣ Stratovolcano chains (Andes, Cascades, Aleutians) ‣ Trenches (unless filled by sediments) ‣ Deep earthquakes ‣ Tsunamis

GEOSC 10 - Geology of the National Parks When Continents Collide? Appalachian mountain range from Newfoundland to Alabama, and again in Oklahoma. Continents are rarely destroyed - so the story gets very complicated. ‣ A colleague’s office - he never throws anything away, so the piles of papers and books get jumbled up Oceanic crust is created, then destroyed...

GEOSC 10 - Geology of the National Parks

Susquehanna Valley from Space Image courtesy NASA, MISR

GEOSC 10 - Geology of the National Parks Appalachians Complicated About 300 Million years ago, N. America collided with Europe/Africa to create a chain of mountains (perhaps 15,000 ft high?). Similar to what is going on today with India and Asia.

GEOSC 10 - Geology of the National Parks Continent-continent Collision

GEOSC 10 - Geology of the National Parks Mt. Everest, looking N Image courtesy USGS, photo by Gimmy P Li

GEOSC 10 - Geology of the National Parks How to Shorten a Continent... Thrust fault ‣ Shorten up a continent by sliding one part up and over another part. ‣ This is what happened in Great Smokies area.

GEOSC 10 - Geology of the National Parks How to Shorten...(2) Farther north (around here), the rocks “wrinkled up” like a kicked rug. The “rug” is layered (hard and soft layers). As time goes by, the soft layers get eroded and the hard layers form the ridges. Susquehanna valley from space, image courtesy NASA, MISR

GEOSC 10 - Geology of the National Parks Cross Section Through SC

GEOSC 10 - Geology of the National Parks Eventually the Collision Stopped This area spread apart (similar to Death Valley pull-apart. Atlantic Ocean formed... still spreading. Mountains stopped being pushed up. ‣ Erosion scrapes away the tops of mountains and deposits the remains (sediment) in the low areas or in the ocean.

GEOSC 10 - Geology of the National Parks Appalachians Still High... But, mountains have “deep roots.” By the principle of isostasy, mountains that stick up high above the landscape also have a thickened crust below them that sticks down into the mantle.

GEOSC 10 - Geology of the National Parks Isostasy, Erosion, Icebergs... As these mountains are eroded, they remain high because material from below is rising up. Like an iceberg floating in water. ‣ Chop off the part above water ‣ Part below water will rise up. - It will be almost as high. - Depends on the density difference.

GEOSC 10 - Geology of the National Parks Plate Collisions... Pull-apart (saw that first week - Death Valley) Subduction (saw that last time - Crater Lake) Obduction (this time) Slide-past (San Andreas fault) ‣ Saw this briefly when we talked about earthquakes

GEOSC 10 - Geology of the National Parks Slide-past Tectonics Sometimes 2 plates slide past each other. ‣ Usually not smoothly (stick slip... and offset of fences, etc.) If there is a “kink” in the boundary, then the sliding-past behavior can make mountains. ‣ The 2 plates push together at the kink rather than sliding past (as they do on the straight bits) ‣ Or the 2 plates pull apart at the kink...

GEOSC 10 - Geology of the National Parks Project Habakuk During WW2, proposal to build an aircraft carrier from an iceberg. Mixture of wood pulp and ice. Small one built on Lake Louise in Canada.

GEOSC 10 - Geology of the National Parks Rocky Mtns - Leading Idea Collision of N. America with oceanic crust. Normally oceanic crust will subduct under continental crust. But, if the oceanic crust is hot, it will slide under the continent, but scrape along the bottom. ‣ Continent gets deformed way inland ‣ Rockies are 1500 miles from the Pacific

GEOSC 10 - Geology of the National Parks Rocky Mtns - Leading Idea Collision of N. America with oceanic crust. Normally oceanic crust will subduct under continental crust. But, if the oceanic crust is hot, it will slide under the continent, but scrape along the bottom. ‣ Continent gets deformed way inland ‣ Rockies are 1500miles from the Pacific.

GEOSC 10 - Geology of the National Parks Cross Section of West Used to be far offshore Warm Cold Push up far inland

GEOSC 10 - Geology of the National Parks Metamorphic Rocks Some rocks in the Rockies and Great Smokies are metamorphic rocks. ‣ Means they have been changed from their original form. ‣ Under the heat, pressure, and chemical action, they change from (usually) sedimentary rocks to a harder, more-resistant rock. - They have been “cooked” ‣ The look different - folded, squeezed, with pretty colors (and funny names).

GEOSC 10 - Geology of the National Parks Metamorphic Rocks

GEOSC 10 - Geology of the National Parks Igneous Rocks Andesite, courtesy USGS Pele’s Hair, courtesy USGS

GEOSC 10 - Geology of the National Parks Why are They at the Surface? As the overlying rocks get eroded and removed, the deeper rocks rise up. The deeper rocks rise up because of isostasy. ‣ Like the iceberg rising up as the part above water is lopped off, and the alien emerging...

GEOSC 10 - Geology of the National Parks Rock Cycle Courtesy USGS

GEOSC 10 - Geology of the National Parks Types of Rocks Igneous rocks ‣ Formed by melting and then solidifying of magma ‣ Or during a volcano Sedimentary rocks ‣ Formed by erosion of other rocks and then deposition Metamorphic rocks ‣ Formed by “cooking” rocks

GEOSC 10 - Geology of the National Parks Hazards Most of us will die of old age. About 1% or fewer die of “outside causes” ‣ Car crashes and handgun deaths. The main geologic hazards. ‣ Tsunamis, volcanoes, earthquakes, landslides. Wear a seatbelt

GEOSC 10 - Geology of the National Parks Tsunami Warning Because the water wave can take minutes to hours to get across the ocean to land, there is time for warning. The earthquake/landslide/meteor strike can be detected almost immediately, so we can send out warning by radio/internet/smoke signals.