At one point in the film (the piece we will be dealing with here) near Grandmas house, the roads are all blocked with lava and fallen rocks, while a large lava spill is heading down the mountain threatening to engulf grandmas house! The only escape is to use the lake Grandmas house is near to. So they get on a small motor boat and speed off along the lake away from the danger.
All seems to be going well till it becomes obvious that the lake has been changed in some way due to the volcanic activity. The boat starts to erode and react, the prop gives out and they just manage to get to shore before the rivets on the boat give way and it sinks to the bottom of the lake!
So is this likely and at all possible? Well first of all can a lake be turned acidic by volcanic activity? The answer is yes, at least in principle. It is possible that sulphur based chemicals would be dispersed onto the lake by the ash from the Vulcano. It is also possible that hot gas pushing up from below would crack through the bottom of the lake and bubble up dissolving in the water. Oxides of Sulphur can produce sulphurous and sulphuric acids in this way. However there is a twist in the chemical tale. The boat in the film is aluminium and although aluminium is a very reactive element it naturaly forms an oxide layer in air which (although very thin, only a fraction of a millionth of a meter think) protects the metal in most practical cases. Further to this sulphuric acids do not attack aluminium greatly so the whole thing looks un-realistic scientifically.
However in the extremely hot reactions and process occurring within a vulcano there are likely to be other gas's produced in the processes including Hydrogen Chloride which forms hydrochloric acid on contact with water. Now this does attack aluminium very reactively. In fact many acids do attack aluminium, especialy when hot and you should rfofr example never cook oranges or other citrus fruit in aluminium pots for this reason (which is why marmalade is not made in aluminiuum pots)! Further to this the lake would be very hot with all the activity. A reaction roughly doubles in pace for every 10 degrees rise in temp. so a hot lake would react extremely quickly with the reactive aluminium. This we showed on the Hollywood Science film using aluminium backing foil and a test tube of heated acid.
So I think it is possible for an aluminium boat to be eroded very quickly by a hot acid lake - once the aluminium starts to react it goes very fast indeed!
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