Haigh, Martin, and Svetlana Gentcheva-Kostadinova. “Geomorphological Impact of Erosion Control Measures on a Steep Coal-Spoil Embankment, Pernik, Bulgaria”. Geografia Fisica e Dinamica Quaternaria 30, no. 2 (December 31, 2007): 179–183. Accessed January 12, 2026. https://www.gfdq.glaciologia.it/index.php/GFDQ/article/view/324.