Endogene processes and landforms NGEA01, 2018

Transcription

1 Endogene processes and landforms NGEA01, 2018 Cecilia Akselsson Department of Physical Geography and Ecosystem Science Lund University

2 Endogene and exogene processes () Endogene/Internal/Constructive/Ulifting Exogene/External/Destructive/Down-wearing

3 Litterature -The Chapter Introduction to landform studies (The study of landforms and forward) -The chapter The internal processes

4 Endogene processes -Plate tectonics -Volcanism and intrusive igneous features -Folding, faulting and earth quakes

5 The structure of the earth ()

6 Plate tectonic theory The lithosphere consists of rigid plates, km thick, floating over the astenosphere

7 Plate tectonic theory Evidence for continental drift 1. Continent edges fitting together

8 Plate tectonic theory Evidence for continental drift 2. Similar geology and fossiles on both sides of the ocean (e.g. the freshwater swimming reptile Mesosaurus

9 Plate tectonic theory Evidence for continental drift 3. Scandinavian, British and American mountains match up (similar age and structure)

10 Plate tectonic theory Evidence for continental drift 4. Glacial deposits indicate glaciation of many parts of the southern hemisphere 300 million years ago

11 Plate tectonic theory Seafloor spreading from mid-ocean ridges, subduction in trenches explains how continenal drift occurs

12 Plate tectonic theory Seafloor spreading also explains the pattern of mid-oceanic ridges, trenches and earth quakes

13 Plate tectonic theory Evidence off seafloor spreading 1. Paleomagnetism - The earth s magnetic field has switched many times, can be seen on the orientation of the iron-rich grains on the seafloor. Symmetry around the ridges. Evidence off seafloor spreading 2. Sea floor cores show that the age of the fossiles increased with increased distance to the ridges.

14 Plate boundaries where the action happens Divergent boundaries constructive boundaries, magma wells up, volcanic activity Convergent boundaries Transform boundaries destructive boundaries, Removal or compression of the surface. Creates mountain ranges, volcanos and trenches two plates slipping past each other laterally

15 Convergent, divergent and transform boundaries

16 Divergent boundaries -Mid-oceanic ridges, with earth-quakes, volcanoes and hydrothermal metamorphism Example: Mid-Atlantic ridge -Continental rift-valley Example: Great East African Rift Valley

17 Convergent boundaries - Oceanic - continental convergence - Oceanic oceanic convergence - Continental continental convergence

18 Oceanic continental convergence Ocean plate underrides continental plate subduction. Mountain range on land (e.g. the Andes), trench in the ocean. Earth quakes and volcanoes continental volcanic arc

19 Oceanic oceanic convergence Oceanic plate underrides another oceanic plate subduction. Oceanic trench, earth quakes, volcanoes, volcanic island arcs with time developing to mature islands, like Japan.

20 Continental continental convergence No subduction. Mountain ranges, earth quakes and metamorphism. Example: Himalaya formed 45 million years ago, when the India plate collided with the rest of Euroasia

21 Transform boundaries Two plates slipping past one another laterally creates transform faults. No creation or destruction of crust. Earth quakes. Example: San Andreas Fault.

22 Plate movement the last 200 million years

23 Other effects of plate movement: 1. Hot spots The mantle plume theory: Volcanic activity far from plate boundaries, caused by plumes of heated material rising through the mantle. The plate moving causes a row of volcanoes. Example: Hawaii.

24 Other effects of plate movement: 2. Accreted terrains Lithosphere carried with a moving plate. Rock type differs from the surroundings. Example: Western part of North America

25 Volcanism short facts - Occurs at plate boundaries and hot spots - Ca 550 active volcanoes in the world - 75 % in the Pacific ring of fire

26 A volcano in Skåne: Jällabjer, ca 150 million years old Photo: Jonas Åkerman

27 Different types of magmas, and eruptions - Felsic magma: High Si content. Thicker, cooler than other magmas. Gas trapped leading to high pressure. Explosive eruptions, pyroclastics. Thick slow-moving lava flows of rhyolitic composition. - Mafic magma: Lower Si content, hotter, more fluid. Gas can move up more easily. Great but quiet outpouring of basaltic magma. - Intermediate magma. Intermediate Si content. Andesitic magma, the way of eruption is in between felsic and mafic.

28 Shield volcanoes (Sköldvulkaner) Broad, gently sloping mountains. Quiet eruptions of fluid lava, usually basaltic. Consists of layers of lava flows. Example below: Mauna Loa and Mauna Kea in Hawaii.

29 Stratovolcanoes/Composite volcanoes (Stratovulkaner) High steep sided cones. Explosive eruptions of pyroclastics and quiet eruptions of lava. Often andesitic. Examples: Mt Fuji in Japan, Mt Vesuvius in Italy and in Mexico (below)

30 Lava domes (Lavadomer) Small (often < 600 m), sometimes irregular. Consists of thick lava, squeezed up in a volcanic vent. Often covered by pyroclastics. Often rhyolitic. Example: California

31 Cinder cones (Konvulkan) Small, steep-sided cone, max height 500m. Pyroclastics ejected from central vents, sometimes also lava flows. Varying chemistry, often basaltic. Example: Hverfjell (Iceland) Photo: Olle Westling

32 Eyjafjallajökull putting Iceland on he world map Stratovolcano with a glacier on top. 2010: 800 persons evacuated. Flight restrictions in large parts of Europe for several days.

33 Bárdarbunga Stratovolcano under the Vatnajökull glacier. >2000 m high. Earthquakes and eruptions from aug 2014 to feb 2015.

34 Intrusive igneous features - plutons

35 Faulting

36 Faulting Breaking apart and displacement of rock structures, Thingvellir, Iceland Photo: Cecilia Akselsson

37 The ridges in Skåne faults along the Tornquist zone

38 Folding Caused by lateral compression, e.g from plate movement Photo: Jonas Åkerman

39 Earth quakes Vibrations often caused by faulting

40 Haiti earth quake 2010: 7.0 on the Richter scale

41 Earth quake in Skåne december 2008: 4.7 on the Richter scale

42 Geomorphology around the world Periglacial processes Polygon wedge ice (Iskilspolygoner): Svalbard Glacial processes Esker (rullstensås): Dalarna, Sweden Photo: Jonas Åkerman Photo: Jonas Åkerman Endogene processes Volcano, Mexico Mass movements, fluvial processes, coastal processes Braided (Flätad) channel, New Zeeland Eolian processes Dunes: Namibia