The history of slag heaps

History buffs see mounds as deserted cities and burial pyramids fro the ancient world, but one overlooked aspect of modern life is that the world is dotted with similar artificial islands due to the waste from mining and steel production.

Atlas Obscura has an article on this overlooked form of modern waste disposal (or sometimes careless lack of proper waste disposal).

Artificial mountains have sprung up all over the world, the result of hellish manufacturing processes, piled construction and mining waste, or in some cases built deliberately to add a humongous new feature to the horizon.

The majority of the artificial mountains in the United States are the byproducts of cement and steel production, formed at the height of those industries between the late 1800s and mid-20th century. ... 

read the whole thing, which also discusses the recycling material from the mounds and the way that they are converted into scenic hills despite some attempts resulted in problems.

when I worked in Pennsylvania, our home was within walking distance of the local slag heap. They had panted trees along it to prevent it from collapsing, but I always wondered about it, and about the red (iron) pollution in our local creek, which had trout upstream but was dead downstream.

On the other hand, it hadn't collapsed even in the 1977 flood, so presumably it is stable.

Webster dump 1940s

Also when I worked in Africa, the local landscape was flat, and we could see the slag heap 30 miles south of us where there was an asbestos mine.

Mashava mine

it would be nice to condemn all these sites, but the dirty little secret is that the modern world wouldn't have existed without them.

The real solution is recycle and proper disposal so that the toxic wastes don't destroy the neighborhood.