Luis Quinta / Storm waves off the coast of Praia do Norte, Nazare, Portugal. January.

Luis Quinta / Abstract image of large sea swells hitting the rocks, Portuguese southwestern coast, Portugal, March, 2010.

Luis Quinta / Surfer riding a big wave, Praia do Norte, Nazare, Portugal, December 2014.

Nick Upton / Sequence 3 / 4. Cleg fly / Horsefly (Haematopa pluvialis) excreting excess water as it swells up with blood sucked from photographer's arm, Wiltshire pastureland, UK, June.

Philip Stephen / Silhouette of the fishing vessel Carisanne battling through heavy sea swells in the North Sea, May 2007

Philip Stephen / Wave breaking over bow of fishing vessel Carisanne as she battles heavy sea swells in the North Sea, May 2007

Harley Betts / Swells at high tide crash against sandstone cliffs, Tongaporutu, north Taranaki, New Zealand

Norbert Wu / Swell Shark (Cephaloscyllium ventriosum) swells up as defense, California

Norbert Wu / Porcupinefish (Diodon sp) swells up in defense, Philippines

Norbert Wu / Swell Shark (Cephaloscyllium ventriosum) underwater, so named because it swells up as defense against predators, California

Onne van der Wal / 12m yachts racing through the swells in the 2006 12 Metre North American Championships, Newport, Rhode Island, USA.

Philip Stephen / MFV "Demares" dipped in the trough of a wave during moderate swells in the North Sea. November 2006.