The rare celestial combination first involved the convergence of a spring tide and a perigean tide
. Spring tides occur at both new Moon and full Moon, when the Sun, Earth, and Moon line up, and the tide-raising forces of the Sun and Moon combine for a greater net effect.
Perigean tide. A spring tide occurring monthly when the Moon is at or near perigee of its orbit.
Indeed, in this region, high perigean tides levels can be anticipated at intervals of 1 month, 7 months, 4.5 years and 18 years.
The perigean tides
' effect on the number of icebergs really was incidental.
A supermoon or perigee full Moon brings with it extra-high "perigean tides
Overlapping of the cycles of spring and perigean tides every 206 days results in an annual progression of 1.5 months in the periods of especially high tides.
These so-called perigean tides recur every anomalistic month of 27.555 days.
Consequently, the tidal variations caused by once-monthly so-called perigean tides are much more prominent.
24, perigean tides at Herring Cove in 1998 coincided with one of the month's set of spring tides around 19 February.
The 206-day cycle of perigean tides coincident with spring tides occurs all over the world, but it is far more pronounced (and far more important) in the Bay of Fundy because of the great tidal range.
Peaks of perigean tides
and spring tides coincide in cycles of 206 days.
A 13th-century treatise described spring tides by saying that "when the Sun and Moon are in conjunction, the power of the Moon becomes stronger and the tide increases and becomes strong." The same work referred to perigean tides
by observing that when the Moon "approaches the point nearest the Earth, its power increases, and then the rise of the sea is strong." Several treatises associated a period of high tides with the winter solstice and therefore, indirectly, with the time of closest approach between the Earth and the Sun.