Abstract
Magnetite is a type of iron ore and a valuable commodity that occurs naturally in black sand beaches in the Philippines. However, black sand mining often takes place illegally and increases the likelihood and magnitude of geohazards, such as land subsidence, which augments the exposure of local communities to sea level rise and to typhoon-related threats. Detection of black sand mining activities traditionally relies on word of mouth, while measurement of their environmental effects requires on-the-ground geological surveys, which are precise, but costly and limited in scope. Here we show that systematic analysis of remote sensing data provides an objective, reliable, safe, and cost-effective way to monitor black sand mining activities and their impacts. First, we show that optical satellite data can be used to identify legal and illegal mining sites and characterize the direct effect of mining on the landscape. Second, we demonstrate that Interferometric Synthetic Aperture Radar (InSAR) can be used to evaluate the environmental impacts of black sand mining despite the small spatial extent of the activities. We detected a total of twenty black sand mining sites on Luzon Island and InSAR ALOS data reveal that out of the thirteen sites with coherence, nine experienced land subsidence at rates ranging from 1.5 to 5.7 cm/year during 2007–2011. The mean ground velocity map also highlights that the spatial extent of the subsiding areas is 10 to 100 times larger than the mining sites, likely associated with groundwater use or sediment redistribution. As a result of this subsidence, several coastal areas will be lowered to sea level elevation in a few decades and exposed to permanent flooding. This work demonstrates that remote sensing data are critical in monitoring the development of such activities and their environmental and societal impacts.
Highlights
There are two types of iron ore most commonly used in the production of steel worldwide: hematite (Fe2 O3, 69.9% Fe) and magnetite (Fe3 O4, 72.4% Fe)
We collected a list of known mining sites from various sources, including contacts on the ground, online news articles reporting either illegal mining activity or community protests related to illegal mining, and reports issued by the Philippine Mines and Geosciences Bureau (MGB) listing mining permits
We evaluate areas associated with land subsidence to be at sea level elevation and, permanently flooded the elevation based on the and on the Global and present this “time until flooding” so decision-makers can gain a sense of the time scales involved
Summary
There are two types of iron ore most commonly used in the production of steel worldwide: hematite (Fe2 O3 , 69.9% Fe) and magnetite (Fe3 O4 , 72.4% Fe). Hematite deposits have been accessible and largely exploited until the last decade. Depletion of these deposits led to an increased demand for magnetite as the need for high-quality iron products continues [1,2]. In the Philippines, magnetite occurs naturally in black sand, which results from the weathering and erosion of metamorphic and igneous rocks. Black sand accumulates in streams and drainage systems and is carried and deposited onto beaches. Much of the Philippine coast is composed of black sand beaches. In response to the demand for magnetite, black sand mining and processing activities have significantly increased in recent years and the extracted magnetite is largely exported to China’s steel mills [2,3]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
