S1, E3: The geological forces at work in Galapagos are complex and unpredictable; so too are the many ocean currents that unite here. Among the 13 islands and over a hundred rocky outcrops and islets, nowhere is more unforgiving and more unpredictable than the island of Fernandina, crowned by the most active of all volcanoes. Yet female land iguanas are forced to climb over 1,000 metres to its summit to find the only warm, soft sandy patches in which to lay their eggs. The ever-changing islands, with eruptions occurring every few years, make it hard to find a foothold. But mangroves are inventive pioneers, their salt-tolerant seeds settling on unforgiving lava terrain to create dense labyrinths of vegetation which are crucial nurseries for fish, offering precious shade from the equatorial sun. Even on the most exposed shorelines, fur seals find daytime shelter in lava grottos, formed by volcanic lava flows. The remotest island, Roca Redonda, is little more than 300 meters tall but it still forms an important platform for nesting seabirds. Like all the other islands, under-sea exploration reveals that its just the summit of an enormous undersea volcano.