Francis Pearce of Dunedin asks :-
What would be the feasability of getting rid of unwanted waste by dumping them into active volcanoes such as in Hawiai?
James White, a volcanologist at Otago University, responded.
Volcanoes are where molten rock rises to the earth's surface from melting sites deep underground. Some active volcanoes, like Kilauea in Hawai'i, erupt the molten rock as fountains of lava, but others violently erupt a mixture of gas and particles formed as the molten rock is shattered. Even Kilauea has erupted explosively at some times in the past.
If we put waste into an active volcano, several things could happen. If there is an open lava pool in the volcano, dense, radioactive waste would sink into the lava and melt, making the lava radioactive. Ordinary waste would simply burn. Kilauea lava is around 1,200°C, near the upper end of temperatures in commercial incinerators.
In commercial incinerators, waste is forced to burn evenly and almost completely, but this wouldn't happen in a volcano because molten rock is more dense than most waste, and typically has a thin crust with a temperature of only a few hundred degrees. The waste would float and smoulder, releasing a lot of smoke into the air. Often, even in active volcanoes, lava deep in the volcano is covered with a thick rigid crust, and buried under debris from the crater walls. Throwing waste in this kind of volcano would just store it inside the volcano until it next erupted, possibly spreading the waste over thousands of kilometres. In the end, the problem is that active volcanoes erupt. Anything we put into them, if it doesn't burn immediately, will come out in the next eruption one way or another.