After the Antarctic Ozone Hole was discovered, some scientists took the view that it might be a natural event caused by volcanic chlorine emissions from Mount Erebus rather than manufactured chlorinated chemicals. Eventually, however, Mount Erebus was exonerated (Zredna-Gostynska et al., 1993). Most of the chlorine Mount Erebus throws up takes the form of hydrogen chloride (HCl), which (like other chlorine from natural sources) readily dissolves in the water vapour of the lower atmosphere well before it can reach the stratosphere.
For Mount Erebus to affect the ozone layer, the volcano would have to inject a large proportion of its hydrogen chloride directly into the stratosphere, above a height of about 10 km. Mount Erebus has been active since it was first observed by James Ross in 1840, but appears never to have erupted with the force necessary to send chlorine directly into the stratosphere. The mountain itself is almost 4,000 m high (3,794 m), but the volcanic plume seldom rises above 5,000 m. The amount of gas Mount Erebus emits also bears no relation to the size of the ozone hole. In the summer of 1983, chlorine emissions from Mount Erebus were about 170 tonnes a day. In the following seven summers, when ozone depletion was even more severe, the chlorine emissions ranged from one-tenth to one-quarter of the 1983 figure (Zreda-Gostynska et al., 1993).