IT WAS love at first sight when Dr Hazel Rymer set eyes on the object of her affection. She had carried a heavy back-pack as she climbed up the steep path which took her to the top of a mountain in Central America. Hot and tired, she eventually reached the summit. She peered over the edge and was suddenly face to face with a bubbling cauldron of molten rock.

Dr Rymer loves volcanoes, and in her job as a Royal Society research fellow in geophysics at the Open University she has visited and studied many examples all over the world. But the first one she saw, Poas in Costa Rica, remains her favourite. "It was a truly magical, fantastic sight - the colours were absolutely stunning. There is something awe-inspiring about volcanoes. They were here long before we arrived and they will be here long after we are gone."

Impressive but also very dangerous. However, Dr Rymer says she has never been scared when standing close to the edge of a volcano. "I do not go out on a volcano when there is anything really nasty going on," she says. "I have been near lava flows and small explosions but I have never felt in any immediate danger. The only risks are those you take whenever you climb a mountain. You are going up steep cliffs and it doesn't help that you are carrying heavy equipment."

The equipment she takes is like a more sophisticated version of a spring balance that can be found in the vegetable section of a supermarket. "What we are doing is measuring minute changes in gravity caused by movements of rock beneath the surface. If you weigh a pan of apples at one end of a market stall you expect them to weigh the same wherever you go. On a volcano the number of apples remains the same but they weigh more or less depending on what is going on inside."

Each volcano will behave differently depending on factors such as the temperature, volume and chemical composition of the molten rock or magma within. By carrying out detailed measurements geophysicists hope to predict if and when a volcano is likely to erupt.

Active volcanoes have always had an important influence on human development. The risks of establishing a settlement too near an active crater are only too clear to anyone who has visited the remains of the Roman city of Pompeii which was destroyed when Mount Vesuvius erupted in AD 79. The huge volumes of gas and dust spewed out in a major eruption can even cause changes in global climate patterns.

The rocky outcrop known as Arthur's Seat in the middle of Edinburgh is the remains of an extinct volcano. But there are no longer any active examples in the UK and certainly none within easy reach of the Open University's home in Milton Keynes. "I always say that the best thing about studying vulcanology in Britain is that you have to travel to do it - the nearest ones are in Italy or Iceland," Dr Rymer says.