EESA06H3 Lecture Notes - Lecture 7: Lahar, Middleton Island, Stratovolcano
Lecture 7: The Death of Oceans – Toward the next supercontinent
Subduction and Volcanic Arcs:
• When two plates (older and thicker → denser gets subducted). The subducting plate → rock
melts → creating rising magma that forms volcanoes.
• Enough of volcanoes and magma that is cooled when in contact with water forms volcanic
islands arcs.
• Accretionary wedge – sediments being scrapped off as it is being subducted (subducting plate).
o Contains lots of oil and gas.
o Very soft (edge will slump – fail
o One of main contributor to making tsunamis (moves the water as it slumps)
• The volcanic island – continental crust (as basalt is melted and seawater is added → adesiti
magma (tend to float)
o Continent-in-the-akig → ill fo soethig like Japan
o Long-te fate → to e pushed oto a otiet to hih it is ollidig
o Possile idiato of ho otiets foed eal o i Eath’s histo
Japan – Subduction Central:
• Where three plates meet (maybe another one diffuse along North American and Eurasia plate)
o Pacific plate being pushed below the Philippines plate (deep ocean trench marking
subduction zone)
o Volcanoes – Japa is olai islad a
o All that pushed against Eurasia plate.
• Japan – has a lot of active volcanoes (erupt every 5-10 years) and a lot of earthquakes (along
subduction zones)
• The data of previous earthquake occurrences in Japan → a statig poit i peditig futue
earthquakes (along deep-water trench at subduction zone) and frequency of earthquakes.
• Seismic gap – where no movement between the two plates and all the energy is stored and
eleased he plates uukle ad esults i ega eathuakes agitude -9).
• Neodani fault – from the Nobi earthquake of 1891 – has different materials on both side of
fault. The earthquake → thee as etial displaeet ad hoizotall alog the
fault.
• The Great Kanto Earthquake (and fire) – flatten Tokyo – Sept 1st, 1923
o Date eeeed Eathuake Pepaedess Da
• March 11, 2011 Earthquake – deformation and the uplift and subsidence of the ocean floor (~1-
7m uplift) and movement toward Japan (more of accretionary wedge – tilted sea floor toward
land [earthquake gained height] – tsunami magnified)
• Chikyu – vessel that drilling down offshore and putting monitors in bed to measure water
pessue suoudig aea, seisi atiit → for early warning.
• Yougest pat of oea floo → alog speadig etes. As ou oe aa fo speadig
centre, age becomes older for ocean floor.
The Aleutian Volcanic Arc and Wrangell Arc of Alaska:
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Lecture 7: the death of oceans toward the next supercontinent. Subduction and volcanic arcs: when two plates (older and thicker denser gets subducted). As (cid:455)ou (cid:373)o(cid:448)e a(cid:449)a(cid:455) f(cid:396)o(cid:373) sp(cid:396)eadi(cid:374)g centre, age becomes older for ocean floor. So close to ocean (a tidal glacier): results from uplift of that part of north american plate above the subduction zone, wall/obstacle preventing moisture (temperate conditions) from going to north america. Shows uplift of oceanic crust/island during major earthquakes: helps with frequency of earthquakes and uplift rate (3. 5m every 100 years). Cascadia subduction zone between pacific plate and juan de fuca plate (most already subducted) and spreading centre off the coast. The plates are locked (cid:894)(cid:374)o (cid:373)o(cid:448)e(cid:373)e(cid:374)t(cid:895) lot of st(cid:396)ai(cid:374) (cid:271)uildi(cid:374)g up a(cid:374)d (cid:449)he(cid:374) the(cid:455) u(cid:374)(cid:272)ouple (cid:373)ega ea(cid:396)th(cid:395)uake and lots of uplift and subsidence: seatle fault (cid:862)(cid:271)li(cid:374)d faults(cid:863) (cid:271)u(cid:396)ied u(cid:374)de(cid:396) sediments. Might become active after earthquakes: vancouver low risk from a large magnitude ea(cid:396)th(cid:395)uake.
