Jokulsarlon lagoon. The Breidamerkurjokull glacier has been retreating since about 1920. The lagoon formed at the glacial front shows a yearly increase.| J-STAGE
Basaltic lava field, the Svartshengi geothermal power plant (right), and the Blue Lagoon (left).| J-STAGE
The braided course of the Jokulfell downstream from Hofsjokull.| J-STAGE
Valley of Eldgja. The 934-40 Eldgja eruption occurred along a 75 km-long fissure.| J-STAGE
Normal fault at Thingvellir. The boundary between the North American plate on the left-hand side and the Eurasian to the right.| J-STAGE
Geyser Strokkur. The geyser erupts at 5-10 minute intervals.| J-STAGE
Gullfoss waterfall. The two-step cataract has a total drop of 32 m.| J-STAGE
Palagonite ridge formed by subglacial eruption. Langjokull glacier in the background.| J-STAGE
Dettifoss waterfall. The waterfall is 44 m high. The river water is rich in suspended sediments and the waterfall volume is the greatest in Iceland.| J-STAGE
Lakagigar fissure eruption. The 1783-84 Laka- gigar eruption resulted in a great famine, due to which Iceland lost 20% of its population.| J-STAGE
Reykjavik is a smokeless city. Almost 100% of the electricity and the heating depends upon hydropower and geothermal energy.| J-STAGE
Earth hummock. Earth hummocks are among the periglacial phenomena. The knoll covered with vegetation is |about 0.5 m high.| J-STAGE

Latest Issue

Journal of Geography (Chigaku Zasshi), 2018 Vol.127 No.5

2018 Vol.127 No.5

From Stagnant Lid Tectonics to Plate Tectonics

The cover art is a schematic illustration showing the evolution of the inner earth during the Hadean. The dry Earth was formed at 4.55 Ga. By 4.53 Ga, the mantle had solidified to form a layered structure and stagnant lid tectonics operated. Between 4.37 and 4.20 Ga, the ABEL Bombardment progressed to deliver atmospheric and oceanic components onto the dry Earth. Due to the destruction of the stagnant lid by huge impactors, stagnant lid tectonics transitioned to plate tectonics. By 4.30 Ga, the bi-modal lithosphere (continental crust and oceanic crust) appeared following bombardment to operate plate tectonics. Due to tectonic erosion, the primordial continents (anorthosite, komatiite, and KREEP I basalt) were transported into the deep mantle. The densest KREEP I basalt dripped down to the bottom of the mantle and accumulated (almost all KREEP I basalt should have accumulated at CMB by 4.0 Ga) (Maruyama et al., 2018).

(Shigenori MARUYAMA)

Reference
Maruyama, S., Santosh, M. and Azuma, S. (2018): Initiation of plate tectonics in the Hadean: Eclogitization triggered by the ABEL Bombardment. Geoscience Frontiers, 9, 1033–1048.

Special Issue: The Hadean World (Part I) : The Birth of a Habitable Trinity Planet

Overview of the Special Issue
　“The Hadean World （Part I）: The Birth of a Habitable Trinity Planet”

Shigenori MARUYAMA, Ken KUROKAWA and Yukio ISOZAKI

Journal of Geography (Chigaku Zasshi), 2018, 127(5), 569.

DOI:10.5026/jgeography.127.569

Introduction to the Special Issue
　“The Hadean World (Part I) : The Birth of a Habitable Trinity Planet”

Shigenori MARUYAMA, Ken KUROKAWA and Yukio ISOZAKI

Journal of Geography (Chigaku Zasshi), 2018, 127(5), 573.

DOI:10.5026/jgeography.127.573

Tandem Planetary Formation Theory (Original Article)

Toshikazu EBISUZAKI

Journal of Geography (Chigaku Zasshi), 2018, 127(5), 577.

DOI:10.5026/jgeography.127.577

Newly Proposed Habitable Trinity Concept
　and the Possibility of Life on Mars, Europa, and Titan (Original Article)

James. M. DOHM and Shigenori MARUYAMA

Journal of Geography (Chigaku Zasshi), 2018, 127(5), 609.

DOI:10.5026/jgeography.127.609

Lunar Seismic Tomography and the Early Earth (Original Article)

Dapeng ZHAO, Shigenori MARUYAMA and Yukio ISOZAKI

Journal of Geography (Chigaku Zasshi), 2018, 127(5), 619.

DOI:10.5026/jgeography.127.619

Chemical Composition of the Outer Core (Review Article)

Hiroki ICHIKAWA and Taku TSUCHIYA

Journal of Geography (Chigaku Zasshi), 2018, 127(5), 631.

DOI:10.5026/jgeography.127.631

ABEL Model of the Two-step Formation of the Earth
　and the Significance of ABEL Bombardment to Produce a Habitable Planet
　(Review Article)

Shigenori MARUYAMA, Toshikazu EBISUZAKI and Yoshinori TANGE

Journal of Geography (Chigaku Zasshi), 2018, 127(5), 647.

DOI:10.5026/jgeography.127.647

Geology and Geochronology of Nulliak Supracrustal Rocks in Labrador, Canada:
　The Oldest Supracrustal Rocks and Evidence for the Operation of Plate Tectonics
　(Review Article)

Tsuyoshi KOMIYA, Shogo AOKI and Satoshi YOSHIDA

Journal of Geography (Chigaku Zasshi), 2018, 127(5), 683.

DOI:10.5026/jgeography.127.683

Pattern of Continental Growth and Its Secular Change (Review Article)

Hikaru SAWADA, Yukio ISOZAKI and Shigenori MARUYAMA

Journal of Geography (Chigaku Zasshi), 2018, 127(5), 705.

DOI:10.5026/jgeography.127.705

Search for Hadean Zircon:
　Decreasing the Time Required for Pre-analyzing Processes and Age Analyses
　(Review Article)

Yukiyasu TSUTSUMI, Hikaru SAWADA and Yukio ISOZAKI

Journal of Geography (Chigaku Zasshi), 2018, 127(5), 723.

DOI:10.5026/jgeography.127.723

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