The Blue Hour

The water levels of oceans and some rivers and lakes rise and fall in regular cycles known as tides. The gravitational pull exerted by the moon—and, to a lesser degree, the sun—causes tides. As water levels reach their highest point, a greater portion of the shore will be covered by water; this is known as high tide. Then, water levels will recede until they have reached their lowest point and leave a greater portion of shore uncovered; this is known as low tide. In The Blue Hour, the patterns of tides play a key role in the plot since tides determine when characters can access or leave the island of Eris. Tides can typically be predicted, both in terms of when high and low tide will occur and the tidal range or amplitude (the difference between the water levels measured at high and low tide). As Hawkins depicts, individuals can plan around the times of day when water levels will be low and when they will be high. Tides can be either semi-diurnal (with two roughly equal high and low tides per day) or diurnal (one high and one low tide per day).

A typical island is a landmass surrounded on all sides by water; some islands are joined to a larger landmass (the mainland) by a piece of land (an isthmus or causeway) that is either exposed or submerged depending on the time of day and tidal conditions. A tidal island cycles between periods in which it can only be accessed via water—during high-tide conditions when the connecting land is flooded and impassable—and periods when it can be accessed via land—when low-tide conditions cause the water to recede and expose land. In her novel, Hawkins imagines a fictional island called Eris; in actuality, there are several tidal islands off the coast of Great Britain, including 17 tidal islands in Scotland. Some tidal islands were historically used as military or defensive sites since their unique geography made them relatively easy to defend. In Western Europe, tidal islands have sometimes also been home to important sites of worship: Mont Saint Michel, a famous Benedictine abbey, is located on a tidal island in France, while Lindisfarne Abbey is located on a tidal island off the northeast coast of England. For the monks who originally populated these religious sites, tidal islands provided enough isolation to facilitate a life of holy contemplation without completely severing access to the wider world. By setting her novel on a tidal island, Hawkins plays on similar themes of isolation, artistic devotion, and withdrawal from the social world.