Official 32 - lecture 3
Earth science class. the professor is discussing an area in the US called the Copper Basin.
Basin: 盆地，水盆
Great Basin; Wash basin.
you may not have heard of the copper basin.
it's in the east in the US, in the Tennessee River Valley.
Tennessee State
it got its name because settlers discovered copper there in 1943.
settlers live in settlement.
and soon afterwards, it supported one of the largest metal mining operations in America.
at one time, four mining companies employed 2500 works in the copper basin.
for that time period, it was a huge operation.
this mining operation turned the copper basin into a desert.
in the 1840s, when mining operation started, it was a dense green forest.
but in 1940s one hundred years latter, it was as barren as moon.
efforts to reclaim the land, and restore the basin to fertile valley as it once was, actually those efforts are still on going.
it's been a long and tedious process.
in fact, it was many years before any results were seen, copper mining had gone on there for more than ninety years.
the damage couldn't be reversed overnight.
although I should mention that by 1996 the water in one of the rivers flowing through the basin was clean enough that it was the site of Olympic whitewater kayaking competition.
and that river is still used now for recreation.
recreation: a way of enjoy yourself when you are not working.
but any way, let's analyze the problem.
it wasn't the mining itself that caused such massive destruction.
it was what happened after the copper ore was extracted from the mines.
ore: 矿石
it was a process called heap roasting.
copper ore contain sulfur, and heap roasting was a way to burn away the sulfur in copper, so they would be left with something closer to pure cooper.
Sulfur (or Sulphur) is a chemical element with the symbol S and atomic number 16.
in the process, large vats of raw copper ore are burned slowly for few months, two or three month actually, to lower the sulfur content.
and this burning, let's look at the results, first the mines were fairly remote, so there was no way to bring the coal other fuel to keep the fires going, so they cut down the local trees for fuel.
and like I said, the fires burn for months, it's lot of fires and lots of trees.
deforestation was occurring at a rapid rate.
and it was accelerated by the smoke of burning more.
big clouds of sulfuric smoke, which was toxic to the trees formed over the area.
tree that hadn't been cut for fuel were killed by the fumes.
fume: 烟
the sulfur also mixed with the air, and created the sulfur dioxide, and sulfur dioxide settled in the cloud, fell into the land in droplets of rain, and sank into soil.
this is what we now call acid rain, you have probably heard of it, but no one used the term back then.
anyway, the acid rain created highly acidic soil.
acid n.
acidic adj.
soon the soil became so acidic that nothing could grow, nothing at all.
vegetation and wildlife disappeared.
and it wasn't just the land and the air, it's water too.
what do you think happened to the rivers?
there were no trees to absorb the rain, and there was lots of rain.
so the rain eroded the soil and swept into the rivers, this is called silting when the soil particles were washed into rivers.
silt 淤泥
and silting continued at an alarming rate.
but this was toxic soil and toxic runoff.
the acid and metals in the soil made once clear river flow bright orange.
so it was really that one step in the process of producing copper, the problems just built up and up until there was a desert where a beautiful forest used to be.
let's look at reforestation and land reclamation efforts.