View Full Version : Full moon to cause Mayon to erupt??

2006-Aug-09, 12:17 PM
Moderator note: the posts in this thread have been merged from three separate threads in order to keep the discussion in the same place. See note below (http://www.bautforum.com/showthread.php?p=801717#post801717). - W.

This is the latest news report from Reuters

Volcanologists have warned that Mount Mayon, in the province of Albay, could explode at any time but that the gravitational pull of a full moon could provide the final push.

"To put it in a simple way, it's like it massages a volcano," Ernesto Corpuz, head of monitoring and eruption prediction at the Philippine Institute of Volcanology and Seismology, told Reuters.

A full moon coincided with at least three of Mayon's nearly 50 explosions over the last four centuries, including the two most recent in 2000 and 2001, Corpuz said.

What does everyone think? Does this make sense?
At first I thought garbage, the moon being full is not going to increase its gravitational pull. It's still the same distance away. But then I thought tides. We get king tides when the moon and the sun line up on the same or opposite sides of the earth. At a full moon they are on opposite sides, so is this massaging the earth's crust to encourage an eruption?

What does everyone else think?

(I originally posted this in reply to an older Mayon message but I wanted the title to grab attention and get opinions.)

2006-Aug-09, 01:12 PM
This was posted on the BBC news website today.

Full moon fear for Mayon volcano:-

Experts say Mount Mayon, the most active volcano in the Philippines, could erupt at any time.

But the full moon's gravitational pull could trigger the eruption, they say.

Why do they think the Moon's gravity affects the Earth more when it is full?

Full story here:


2006-Aug-09, 01:47 PM
At the Institute's website (link (http://www.phivolcs.dost.gov.ph/)) there is no mention of this.

Ronald Brak
2006-Aug-09, 02:00 PM
When the moon is full or new it is in line with the sun and their combined pull is greater than at other times. But that's not what the article says, so yeah, I'd say they got it wrong.

Blue Fire
2006-Aug-09, 02:01 PM
Perhaps because of this?:

Few realize that the solid earth also exhibits tidal behavior with bulges on opposite sides of the globe, also driven by the moon. At HVO, we can actually measure these tides with our tiltmeters and strainmeters. The earth's surface tilts up to 0.03 microradians in response to the apparent passage of the moon overhead. A tilt of one microradian is the tilt of a solid bar one kilometer (0.6 miles) long with one end raised by the thickness of a dime. To emphasize how small the tidal tilts are, our tiltmeters automatically alert us to the possibility of volcanic activity when tilts change more than 0.5 microradians in 5 minutes.

Who would have thought that the moon had that kind of power, not only to be able to cause the world's oceans to bulge, but also to squeeze terra firma twice a day? But it does, so it should not come as a complete shock that reputable scientists have suggested that these squeezings might influence whether a volcano will erupt or not.

2006-Aug-09, 04:12 PM
Moved from Bad Astronomy Stories to Small Media at Large.

2006-Aug-09, 05:17 PM
It is on the Reuters website though.

link here (http://today.reuters.com/news/NewsArticle.aspx?type=scienceNews&storyID=2006-08-09T070822Z_01_SP131206_RTRUKOC_0_US-PHILIPPINES-VOLCANO.xml)

2006-Aug-09, 05:24 PM
A story today (http://news.yahoo.com/s/nm/20060809/sc_nm/philippines_volcano_dc_11) claims that Filipinos and "scientists" are worried that a full moon may spark a volcanic eruption. They claim it's due to increased gravitation pull of a full moon...

Is this Bad Astronomy?

I have heard the theory that a moon that passes directly overhead of a volcano (or anywhere for that matter) has a slightly more gravitational pull than when it passes farther away. But what about a full moon, other than a brighter night sky would cause any changes here on Earth?

Some of the supporting quotes in the article cite such rock hard theoretical evidence as "My parents told me that a full moon triggers an eruption...", and that full moons coincided with THREE of the last FIFTY eruptions. Now I'm no statistician, but if full moons happen once every roughly 29 days, isn't two coincidences EXPECTED, and three not that remote a possibility?

Maybe I'm becoming too skeptical....

2006-Aug-09, 05:28 PM
Also, I don't know that it has any bearing, but the full moon and lunar perigee do actually coincide this month (well almost, full moon is on the 9th, perigee is on the 10th).

Nowhere Man
2006-Aug-09, 05:33 PM
This is being discussed in several other threads. Search for mayon and/or volcano.


2006-Aug-09, 05:50 PM
Welcome to the forum, reedster.

Note: several of the above posts were merged from new threads started in the General Science and Q&A sections. Since they follow the same reportage, I thought it'd be easier to consolidate them here.

Previous thread on the same topic:

Mayon volcano erupted (http://www.bautforum.com/showthread.php?t=44358)

Edit: I'd initially had just merged two threads, but added a third so that we don't end up discussing the same topic in multiple places. Sorry for the mess.

2006-Aug-09, 05:54 PM
Here (http://vulcan.wr.usgs.gov/Outreach/AboutVolcanoes/do_tides_affect_volcanoes.html) is the US Geological Survey's take on full moons, tides, and volcanoes. They don't completely dismiss it, but seem to say it is at most a minor effect.

Although this is a fascinating correlation, there are just too many tidal maximums and too many volcanoes to base predictions on tidal cycle alone. In the Hawai'i example of 52 eruptions since January 1832, there have been nearly 3,900 tidal maximums, of which roughly 3,850 of them went by without causing an eruption. Statistically, this is about a one percent chance that any tidal maximum will affect the start of an eruption.

The correlation is more important as a clue to how volcanoes work. The effect of the tides suggests that a volcano can remain in a state of near eruption for a period of time before some threshold is exceeded and an eruption starts. There are probably many possible mechanisms for exceeding that threshold - the lunar tides are but one.

Here (http://news.nationalgeographic.com/news/2002/02/0215_020215_volcanohunter.html) is a National Geographic article about it. It mostly talks about a study of the Stromboli volcanoe in Italy.

The team's task was to determine when the greatest peaks in eruption activity occurred, and what connection the increased activity might have with the moon's gravitational pull. Following the patterns they had seen in the past, the O'Mearas predicted that during the volcano's ongoing eruptions, there would be peaks in volcanic activity at perigee and at full moon. In this case, events bore out that hypothesis and in fact the greatest spike in volcanic activity occurred at a point in time just between full moon and perigee.

As exciting as the O'Mearas' investigations may be, Steve cautions that they cannot be considered independently of other volcanic variables. "We're not saying that by simply following the moon we can predict when a volcano will erupt," he notes. He does, however, advocate including the moon in the equation for predicting eruptions, with other more traditional variables.

Again, it sounds like a minor variable. What is also interesting is that the peak is not at the full moon.

2006-Aug-09, 05:58 PM
It is on the Reuters website though.

link here (http://today.reuters.com/news/NewsArticle.aspx?type=scienceNews&storyID=2006-08-09T070822Z_01_SP131206_RTRUKOC_0_US-PHILIPPINES-VOLCANO.xml)

All that means is that it's on the wire service. It doesn't mean it's right.

2006-Aug-09, 06:02 PM
I'd expect there to be a correlation with both full and new moons, not just with the full moon. I.e. whenever lunar and solar tides coincide. Water tides are at their highest during the "Proxigean Spring Tide" when the new moon is at perigee. Wouldn't "earth tides" be highest then, too?

2006-Aug-09, 07:10 PM
Selden: 'Wouldn't "earth tides" be highest then, too?'


As to the earth tides effecting volcanoes, Swifts post fairly well covered it.

The magma pools that live under volcanoes are compressed then expanded daily as the earth tides occur. This has the effect of making these magma pools into a sort of natural pump. As the magma chamber expands at the high tide it reduces the pressure of the magma, allowing more flow into the chamber from it's tectonic, hot spot, or crest fissure source. Then as it compresses again, the back pressure form it's sorce prevents the magma from being pumped back out the same way. This is one of the mechenism's that leads to magma pools growth.

However it is a minor one compared to the steady flow that it's source will always pump into the chamger, maybe only 2% of total flow at most.

Can the moon triger a volcano eruption? Sure can, any number of things can be the trigger.

In the case of Mt. St. Helens it was the Mag 5.4 earth quake/land slide that triggered the susequent eruption.

Compartively to that earth quake, the pull of the moon on the land would come in at the power of say a .0295 on the ricter scale.

It possibple moon cycles might cause an eruption, but as USGS and National Geogric said, it's just one of many contributing factors, and one of hte least likely of them.

2006-Aug-09, 07:39 PM
The BA has weighed in (http://www.badastronomy.com/bablog/2006/08/09/mooning-a-volcano/).

2006-Aug-09, 08:17 PM
All that means is that it's on the wire service. It doesn't mean it's right.

I know, and because of the merged threads my comment here is out of context. When I originally replied I was merely confirming the article was on Reuters since the OP in the thread I was responding to did not link the article. I am well aware that a news service is not proof of scientific fact.

grant hutchison
2006-Aug-09, 10:27 PM
For anyone who wants to do their own analysis, there's an eruptive history of Mayon here (http://www.volcano.si.edu/world/volcano.cfm?vnum=0703-03=&volpage=erupt&VErupt=Y&VSources=Y&VRep=Y&VWeekly=Y).

I pulled 41 more-or-less usable start dates off the list, and typed them into an astronomy simulator, my venerable copy of Dance of the Planets. I was pretty generous with what I called a full moon, allowing for lopsided gibbous phases, maybe three days either side of full. Interestingly, six out of the last seven eruptions on that list came up with this sort of "full-ish" moon, which may account for popular recollection and perception. The count goes down in the long term, though, hitting 13 out of 41 (32%).
Now, the chance of spotting a moon in the phase range I used is only about 20%, suggesting I should have found only eight "full-ish" moons.
However, the sample is too small to say anything useful: the 95% confidence interval on 41 trials with a 20% probable outcome includes the possibility of 13 hits, if I'm doing my sums right.

Grant Hutchison

Disclaimer:: I copied and typed and eyeballed. There may well be some errors in my figures. I hope someone feels the urge to attack these data more scientifically.

2006-Aug-09, 10:34 PM
I know, and because of the merged threads my comment here is out of context.

Sorry about that.

2006-Aug-09, 11:22 PM
Sheeze, it's obvious. You can that there is more moon during a full moon, so that means more mass, and so more gravity. ;)

2006-Aug-10, 04:29 PM

What about New Moons?

grant hutchison
2006-Aug-10, 05:48 PM
What about New Moons?Far fewer: four, if I recall correctly. But the visual criterion for a new moon is rather tighter than my very generous "full-ish" moon: it needed to be a pretty slim crescent before I jotted down "new".
It would be nice to revisit these eruption-start data using a program that gave a precise phase angle, because I'm just estimating the range of "phase space" I'm calling "new" and "full" at present, so the stats are very shakey.
However, I would suggest that the recent run of eruptions starting at the time of "full-ish" moons might explain the social phenomenon that this particular volcano's eruptions have been linked to the phase of the moon. Deciding whether tidal effects really do trigger eruptions would need a much bigger database, and more precise figures for the forces involved, as well as the moon-sun alignment.

Grant Hutchison