No one knows when the Hawaiian lava will stop flowing. Here's why

Most of us have seen the incredible images from Hawaii’s Big Island over the past few weeks: rivers of molten rock creeping slowly and inexorably down hillsides and through residential neighbourhoods, fountains of glowing lava spewing from cracks in the earth.

For the residents of the two communities so far affected - Leilani Estates and Lanipuna Gardens - the situation is bleak. Experts say it could be weeks or even months before the lava stops flowing, and it seems those forced to watch the slow destruction of their property could be left with nothing. The rarity and unpredictability of volcanic eruptions means lava insurance is either unavailable or prohibitively expensive. As one Big Island resident told CNN: "People in Hawaii - the Big Island - have to deal with the lava …. I knew that when I moved here. This was a gamble that everybody takes. I just, maybe, have lost."

As well as the heartbreak caused to individuals and families, the financial cost is sure to be high. According to the US Geological Survey, lava flows from Kilauea - the volcano currently causing problems on Big Island - have been almost constant since an eruption in 1983, which is why it is impossible to predict when the current outpouring of lava will end. By the end of 2016, around 4.4km3 of lava had poured from Kilauea’s summit, covering 144km2 of land and destroying more than 200 buildings.

Volcanic disruption is not limited to ground-level, however. The 2010 eruption of Eyjafjallajökull, a volcano in Iceland, threw plumes of ash into the jetstream, causing large-scale disruption to air travel across Europe. Those two weeks of disruption cost the global economy some $5 billion, according to a report prepared for Airbus by Oxford Economics.

But perhaps the most costly eruption in recent history - in terms of lives lost, as well as economically - was that of Tambora in Indonesia, in 1815. It was the only eruption since the year 1400 to register a 7 on the volcanic explosivity index (VEI); to put that into context, a category 7 eruption is only expected once every few thousand years and is 10 times more violent than a category six.

The eruption of Tambora threw so much ash into the atmosphere that it caused what has come to be known as the year without a summer. Ash clouds darkened skies as far away as northern Europe. Global temperatures dropped by three degrees. Crop yields and food supplies were devastated across the globe, and it is estimated around 92,000 people starved to death as a result.

The VEI tells us we shouldn’t expect another category 7 eruption for at least another few hundred, if not few thousand years. But what about a category 8? There are several supervolcanoes lurking under the earths’ crust, each of which has the potential to be thousands of times more devastating than Tambora. One of the largest lies under Yellowstone National Park, in the western United States. Scientists estimate it should erupt once every 600,000 years or so - and is already 40,000 years overdue. Should it do so, the devastation caused to the US and across the world would be immense.

The events at Kilauea, coupled with some strange seismic goings on in Yellowstone recently, have prompted worries that the supervolcano - which has a crater so large it could contain the city of Tokyo - could be about to blow.

Don’t worry, says the US Geological Survey - the chances of that happening in any given year are 730,000 to one, and there is no activity to indicate an imminent eruption.