Yellow earth - Oudo (English spelling)

Japanese: 黄土 - おうど（英語表記）loess

A homogeneous, porous, loose yellowish brown soil consisting of clay and fine sand. It is also called loess. It is unstratified and vertical cracks have developed due to weathering. It contains a lot of limestone _CaCO3 , which is contained in the form of unique tubercles called loess kozo and ginger stone. The minerals are mostly quartz, with small amounts of clay minerals, feldspar, mica and other colored minerals. It is distributed worldwide, including northern China, Europe, North America, North Africa, and New Zealand. In Japan, there are ancient sand dunes made of loess-like sand near the Genkai Sand Dunes and Yasuoka, Yamaguchi Prefecture. In central Europe, loess is divided into four layers 10 to 20 meters thick, with a layer of moraine created by glaciers between them. Ferdinand Wilhelm Richthofen said in 1879 that Chinese loess was 600 meters thick, but today this refers to the entire red clay layer from the Neogene period onwards, and loess is said to be about 10 meters thick. It is believed that loess was formed when rock powder created by glacial erosion during the Pleistocene was carried by wind during dry periods, but there are also other theories, such as the lacustrine theory and the fluvial theory. Loess has the ability to absorb capillary water, so crops can grow even during dry periods. Because loess is fine-grained, when the wind blows it becomes a "yellow dust cloud," and when suspended in water it becomes the source of the muddy water of the Yellow River and Yellow Sea.

Yellow earth

Please see the "Yellow Earth" page.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

粘土，細砂からなり，均質，多孔質，粗鬆（そしょう）な黄褐色の土。レスともいう。無層理で風化によって縦の割れ目が発達する。石灰分 CaCO₃が多く，これが黄土小僧，しょうが石と呼ばれる特有の結核となって含まれる。鉱物は石英が多く，少量の粘土鉱物，長石，雲母などの有色鉱物を伴う。中国北部，ヨーロッパ，北アメリカ，北アフリカ，ニュージーランドなど世界的に分布する。日本では玄海砂丘，山口県安岡付近にレス状砂からなる古砂丘があるといわれる。黄土は中央ヨーロッパでは厚さ 10～20mで 4層に分けられ，間に氷河による堆石の層がある。中国の黄土は 1879年フェルディナント・ウィルヘルム・リヒトホーフェンが厚さ 600mに及ぶとしたが，今日ではこれは新第三紀以後の赤色粘土層全体をさすもので，黄土は 10m程度と訂正されている。黄土は更新世の氷食によってできた岩粉が乾燥気候の時期に風で運ばれたものとされているが，ほかに湖成説，河成説などもある。黄土は毛管水を吸上げる性質があるので，乾燥期でも農作物が育つ。黄土は細粒のため風が吹けば「黄塵万丈」状態になり，水中では懸濁して黄河，黄海の泥水のもとになっている。