Tides and tidal waves

Little Manly, Sydney, a negligible tsunami.

One of the most important features in the world of a marine animal is the movement of the sea itself. Apart from the wave-action near the surface and the to-and-fro tidal streams in shallow coastal areas, the whole water-mass is in continual flow as part of a greater system of oceanic circulation.
— Sir Alister Hardy (1896 – 1985), The Open Sea: Its Natural History, Houghton Mifflin, 1965.

The sea is calm tonight,
The tide is full, the moon lies fair,
Upon the Straits.
— Matthew Arnold (1822 – 1888), Dover Beach.

A private Letter from Norfolk Island describes the extraordinary rise of the water that took place the 8th of May last in the following words. “At half past three in the afternoon, it being then almost low water, an unprecedented efflux took place in the channel which though seldom containing less water than from 2 to 3 fathoms, in the space of two minutes were left dry, then the water flowing suddenly, beat up against the Barracks, which are more than 20 yards beyond the high water mark, returning with extreme rapidity to its former distance. At each recoil of this tremendous surf the whole space between the channel further than Blockade was laid nearly bare, so as to discover frightful rocks and fragments, that before had never been visible. The water dashed against the barrack pale, & at the next returned reached to their very top, in one dreadful mass threatening destruction to the whole town; and our fears suggested, that had it then broke upon us its fury must have been irresistible: this happily was not the case, though many houses were much damaged, and one swept totally away. This rage of the element continued the whole night; nor did the tide recover its usual flow until the third day following. Between us and the Little Island many rocks appeared at intervals which had ever before been secreted from the eye by a depth of water. In Pigrun Bay, from the exposed situation of which such a rapid surf would be less unaccountable, no difference was visible, nor was any part of the Island, to the eastward of Far Bay, at all affected, tho’ an easterly wind prevailed almost the whole time.”

— The Sydney Gazette and New South Wales Advertiser, 4 August, 1805, 1 – 2.

These unusual tides occur every now and then, and are not thought much of; but by careful enquiry I ascertained that the surf had occurred on the very night I had felt the earthquake at Labuan Tring, nearly twenty miles off. This would seem to indicate, that … the sudden heavy surfs and high tides that occur occasionally in perfectly calm weather, may be due to slight upheavals of the ocean-bed in this eminently volcanic region.
— Alfred Russel Wallace (1823-1913), The Malay Archipelago (1869), 125.

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