Supermoon and the Japan massive earthquake

The massive 8.9-magnitude earthquake and deadly tsunami in Japan has made the story about the supermoon coming up on March 19, 2011 even more difficult to explain. A “supermoon” did not cause the Japan earthquake, but – if bad weather combines with high tides along coastlines – it might cause flooding on March 19. Here’s what’s true – and false – about the supermoon on March 19.

“The Japanese earthquake on March 11 is an example of a supermoon causing earthly effects.”

False. In fact, the March 11 moon shows exactly the opposite, since the moon is not particularly close to Earth on March 11, nor is it full or new moon (aligned with the sun and Earth). In fact, the moon on March 11 is close to first quarter – at a right angle to the Earth/sun line. Thus – according to the supermoon-earthquake connection theory – the moon’s effect on earthly water and solid rock tides should have been at its least on the day of the Japan earthquake.

“The last times the full moon was at perigee was in 1955, 1974, 1992 and 2005.”

False. Full moon and perigee closely realign way more often than that, in periods of a little more than 413 days (about 1 year 1 month and 18 days). Check out this list of perigee full moon distances. There are, of course, differences in how closely the full moon aligns with the moon’s closest point to Earth for the month. On March 19, 2011, there is about an hour difference between the full moon and perigee. On July 21, 2005, the difference was about 9 hours.

“A supermoon caused the December 26, 2004 tsunami in Indonesia.”

False. We all remember the devastating earthquake in the Indian Ocean on that day. It created a tsunami that plowed into coastlines and caused the deaths of more than 200,000 people. The December 2004 tsunami was especially deadly along the coast of Indonesia. In terms of loss of life, it was the worst earthquake and worst tsunami in recorded history. There was a full moon that day, but it was not a supermoon. In fact, the moon on the day of the 2004 Indonesian tsunami was nearly at its farthest from Earth. The moon was closest two weeks later on January 10, 2005.

“Some astrologers and even astronomers are using the term supermoon.

True. What makes it super is that – on the day of the March 2011 full moon – the moon will also be closest to Earth for the month. The March 19 full moon will be 221,567 miles from Earth, in contrast to the moon’s average distance of about 239,000 miles. No full moon will be this close to Earth again until November 14, 2016.

The moon is full every month, and – over the course of every month – there is a connection between full moon and earthly tides. At full moon, the sun, Earth, and moon lie more or less along a line in space. At these times, the gravity of the sun and moon are reinforcing each other. That’s why, every month around the time of full moon, people along the coast experience maximum high (and low) tides known as spring tides. Actually, there are two spring tides each month, one at full moon and the other at new moon, as shown in the illustration below.

What does this mean for the March 11 moon. Nothing at all. On March 11, 2011, the moon is not particularly close to Earth, nor is it aligned with the Earth and sun.

“The term supermoon is new.”

True. I had never heard the term supermoon until recently. According to AccuWeather blogger Mark Paquette the term supermoon originated on the website of astrologer Richard Nolle. Paquette said in early March that a new or full moon at 90 percent or more of its closest perigee qualifies as a supermoon. That makes the March 19 full moon a super supermoon, because the crest of the moon’s full phase comes within an hour of the moon’s closest point to Earth.

“Supermoons cause higher-than-usual tides.”

True. There are typically two high tides and two low tides each day. The difference in height between high and low waters varies in a two-week cycle. Around each new moon and full moon, the sun, Earth, and moon arrange themselves more or less along a line in space. Then the moon’s pull on the tides increases, because the gravity of the sun reinforces the moon’s gravity. At such times, the tide’s range is at its maximum. This is the spring tide: the highest (and lowest) tide. Spring tides are not named for the season. This is spring in the sense of jump, burst forth, rise. So spring tides bring the most extreme high and low tides every month, and they happen around full and new moon.

At supermoons, when the moon is at its closest – and when the sun, Earth and moon are aligned in space – we can indeed have higher-than-usual tides.

“Supermoons cause flooding along coasts.”

Sometimes. Supermoons – new or full moons at their closest to Earth – can combine with bad weather to cause flooding. Close full moons do cause maximum tidal ranges. So if a storm moves into a coastline on the day a full moon is closest, it can cause flooding along that coast. If you live along a coast, and a storm is heading your way on or around the time of a supermoon … expect possible flooding and take precautions.

Bottom line: Did a supermoon cause the massive 8.9-magnitude earthquake and deadly tsunami in Japan on March 11, 2011? No. But supermoons – close full or new moons – can cause flooding along coastlines.

Understanding moon phases