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Open AccessArticle

Satellite ASTER Mineral Mapping the Provenance of the Loess Used by the Ming to Build their Earthen Great Wall

1
C3DMM Pty Ltd., 3/473 Cambridge Street Floreat, Western Australia 6014, Australia
2
Key Laboratory of Digital Earth Science, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100094, China
3
Hengyang Base of International Centre on Space Technologies for Natural and Cultural Heritage under the Auspices of UNESCO, Hengyang 421002, China
*
Author to whom correspondence should be addressed.
Remote Sens. 2020, 12(2), 270; https://doi.org/10.3390/rs12020270
Received: 30 October 2019 / Revised: 7 January 2020 / Accepted: 10 January 2020 / Published: 14 January 2020
(This article belongs to the Special Issue ASTER 20th Anniversary)
The earthen border wall (Great Wall) built by the Ming is largely made of wind-blown loess. However, does the composition of this loess change along the length of the wall in response to variations in regional sediment transport pathways and impacting on the wall’s erosional durability? To date, defining these sediment transport pathways has been a challenge because of the paucity of spatially-comprehensive, compositional information. Here, we show that satellite ASTER mineral maps, combined with field sample measurements along a 1200 km section of the Ming’s earthen wall, reveal both the compositional heterogeneity of loess as well as the complexity of the sediment transport pathways of individual loess components, including: (i) quartz sand from Cretaceous sandstones in the Gobi Desert; (ii) gypsum from evaporative lakes in the Tengger Desert; (iii) kaolinite from Devonian Molasse in the Qilian Shan; and (iv) chlorite and muscovite from meta-volcanic rocks exposed across the Alashan Block. Sediment transport pathways involve a combination of colluvial, aeolian and fluvial (ephemeral and permanent) processes shaped by the topography. ASTER enabled mapping of compositional gradients related to two pathways, namely: (i) quartz sand driven by aeolian saltation in concert with the Yellow River; and (ii) clay and fine silt travelling large distances (>500 km) by long-term wind suspension. The most intact section of wall is found along the Hexi Corridor, which is poor in quartz sand and rich in (kaolinitic) clay and fine-silt, driven by wind-shielding by the Alashan Block. We also found evidence that the Ming: (i) mined loess from close by the wall (<1 km); (ii) targeted loess richer in finer fractions; and (iii) routinely applied a Ca-rich additive (probably lime). View Full-Text
Keywords: ASTER; mineral mapping; earthen Great Wall; loess; Ming Dynasty; sediment transport pathways; mineral system; erosion; deposition; aeolian; fluvial ASTER; mineral mapping; earthen Great Wall; loess; Ming Dynasty; sediment transport pathways; mineral system; erosion; deposition; aeolian; fluvial
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Cudahy, T.; Shi, P.; Novikova, Y.; Fu, B. Satellite ASTER Mineral Mapping the Provenance of the Loess Used by the Ming to Build their Earthen Great Wall. Remote Sens. 2020, 12, 270.

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