Lava is an optimum source of geo-thermal energy. If used sensibly it can replace a lot of fossil fuel burning.
Iceland is perhaps the most energetic place on the planet, and its “problematic” recent eruptions have seriously disrupted aircraft travel in England and Europe, thousands of miles away.
Living (or working) anywhere near an active volcano is hazardous to people or machines, but remotely operated machines are more “expendable” than people are. It is the use of such machinery that makes work possible in their vicinities, with people operating them at a safe distance. I have seen on my television, a man in a hefty furnace “space suit” walk on the hot pumice crust of a volcano to within 10 metres of a flowing river of molten lava to collect a small beaker of that lava on a long stick... It wasn't a wooden one!
The Plan for extracting hot lava from such a stream does not involve such dangerous exploits, but from a moving cable “ski-lift” a high temperature “bucket” is lowered, scoops up material, and is raised again such that the main (moving) cable may be 100 metres above the lava stream and made of conventional steel, and may not need cooling, or else such can be arranged. Only the cable that is lowered and the bucket need to be high temperature capable. Flowing Lava is usually between 1000 and 2000 degrees celcius. The hotter (and more fluid) the better!
Although only a single heavy spanning moving cable need traverse the crater, a loop is desirable to keep cable speed moderately fast (5-10metres/second). The empty bucket return need not traverse the lava stream – it can go around the crater, or can be a second pickup travelling in a parallel path in the opposite direction with a second drop-off point at the opposite side. A wheeled tower on the ridge top allows the (now winched up) bucket to pass over the crater lip and down the outside – to a return wheel further down the outer cable slope, one or both of which can discharge the lava in a “safer” region to where it can be carried down the mountain towards the sea or a lake. TWO carriages on the cable (with winches) about 100metres apart would provide better control of the scoop bucket(s) and some redundancy against “tackle” failure. On this basis each cable carriage (which are normally cool or cooled) may have 2 winches as well as CCTV and other sensors for remote operators to control each of the bucket's collection swoop (provided the moving cable is strong enough) to allow a bucket every 100 metres of cable to pick up a tonne of lava every 20 seconds or so (at 5metres/second) though bucket entry speed could be less than cable speed. That's 3 tonnes per minute, per direction, or up to 360 tonnes per hour, 8,640 tonnes per day
The electrical energy needed to operate the moving cable and the winches is a lot LESS than that gained by the descent of the buckets to sea level in a lava equivalent of hydro-electric power from a high lake, and is the first (but not main) generating potential of the scheme. The main output is thermal energy to drive a mostly conventional steam turbine power house. Whether our 8,000 tonnes per day of white hot lava would produce more energy than burning 8,000 tonnes a day of coal I don't know – perhaps more, perhaps less. But the coal burning would produce about 24,000 tonnes of CO2 a day to do so, and the lava wouldn't.
The effect of extracting 8,000 tonnes per day (about 4,000 cubic metres) from the volcano may lower the level of the lava pond by a metre or so, were it not replenished by up-welling lava as expected, and the unsupported pummice crust may collapse. This should not be a worry (so long as scientists in furnace suits aren't wandering about on it!) but the reduction in pressure of a much bigger drain of lava may cause an eruption and possible loss of equipment. However, as we are removing heat (and mass) the overall result should be to lessen that possibility, or reduce its violence. I don't expect it to “run out of lava” even though we may have to “dip deeper” to fill our buckets. Ask Mr.Spock or a competent vulcaologist! Taking away a significant amount of energy should reduce potential hazard and be beneficial.
RESIDUE – this is useful, if the conventional steam boilers are replaced by (steam generating) casting dies to make desired shaped blocks or extrusions for building purposes from the cooling lava – although it may sound strange and wasteful to further HEAT up the lava (electrically) to make it less gaseous or more fluid, or even to extract metals or wanted materials from it, this added energy is partially recovered by greater steam generation from the die casting or extruding process. Although of little tensile strength, the material has fair compressive strength which can be reinforced by steel or other materials to handle pressure in (for example) 20 metre diameter transport tubes below sea level. Very large structures can be extruded out into the sea, in long float-able lengths (1Km). Temporarily sealed by removable plates, or large interlocking blocks can be made for sea-walls or even domestic and commercial constructions... effectively “for free” as can industrial gasses be gathered.
Portable energy can be had by “simply” transporting hot lava in insulated bulk carrier ships to replace coal or nuclear power plants abroad, such as TMI New York's power source, or the electrical energies used to produce Liquid Nitrogen for SAFELY powering vehicles and houses, particularly for cooling needs and reducing food wastage – see www.PowerStep.Org