You will walk up to the peak of Maunga Pu, approx. 120m above sea level. The terrain is not very difficult, but it can be overgrown and slippery, so please wear at least sandals (no flip-flops). Insect repellent and sunscreen recommended!

Aitutaki, the Tilted Atoll

You will see, why Aitutaki looks as it is today, the difference to other atolls, and you will climb the Maunga Pu, the highest point of the prehistoric volcano.

An atoll is a ring of coral reefs, which encloses a lagoon. The lagoon is generally shallow and warm, the reefs protrude mainly just a few meters from the sea. The name "atoll" comes from "atolhu" from the language of the Maldives. The small coral islands that make up the atoll are called "motu", a Polynesian word for "island". The largest atolls can be found in the Maldives, a country that consists only of atolls.

Maunga Pu, seen from departing flight	View from the lagoon (Samade)

Since corals need relatively warm water, atolls can be found only in tropical regions between about N28° and S25°. Because of their size there is usually no natural fresh water.

Very often, the reefs are the foundations of sandbanks, where palm trees and other vegetation are the starter on the way to form "real" islands.
One of Aitutaki's southern motus, "Honeymoon Island", is a nice example for such a newborn place. Pictures and maps from the early 20th century are showing just shallow, but open water, where you can find a pitoresque little island today. Locals are gently supporting the growth of the islands by planting coconut trees on the beaches.

Origin of atolls

The origin of the atolls was explained by Charles DARWIN during his voyage on the HMS Beagle: Along the shallow coastal area around a volcano there are coral reefs, where the water has an optimal depth. If the water is too deep, too less light penetrates to the ground, if it is too shallow, the corals rise from the water at low tide. So over thousands of years a ring is formed around the volcano.
While (and if) the volcano decents, the corals grow up and maintain a constant depth, while the base is reaching deeper and deeper.
The volcano may disappear completely in the sea, while a ring-shaped atoll remains, or the reef encloses the island, like in Rarotonga or Aitutaki.
In some cases, the earth's crust rises (or the sea level drops) and elevates the inner area above the sea level. This forms a "risen atoll", like the island of Niue.

An alternative explanation, in the absence of an existing island (volcano), comes from the Austrian marine researcher Hans HAAS.
According to his theory, a bank of corals is growing in shallow water. The interior of the coral bank is supplied with less oxygen (compared to the outer regions) due to the poor circulation, are thus "weaker" and may die. If the ground rises, the remaining ring of corals form the atoll.

Environmental fragility

Changing Climate

Atolls are very vulnerable to climatic changes. Rising sea levels, as caused by the global warming, could flood most atolls. The rising CO2-concentration of the atmosphere overacidifies the sea water near the surface. The emerging calcium hydrogen corrodes the lime and threatens the stability of the reef.

Nuclear Tests

After the Second World War remote atolls were used for atom bomb test. The Bikini Atoll (Marshall Islands) was the scene of U.S. tests, the Mururoa Atoll (South Pacific) suffered as a test area for France until the 1990s.

What is special with Aitutaki?

Aitutaki is an "Tilted Atoll": the volcano "got stuck" at its northern end. While the southern part of the island has dropped below sea level, the northern part is still reaching up 120m from the sea.
On the western beginning of the walk onto the Maunga Pu one can clearly see the tilted structure of the massif.

You can compare the origin of a "standard" atoll with a "tilted" atoll from the following picture (the names below some of the pictures are examples for island/atolls of the respective type)

Regular Atoll

A: a reef is growing at a certain, optimum depth around the volcano
B an C: the volcano descents (or the sea level rises) over a long period
D: the volcano has completely disappered below the oceans surface

Tilted Atoll

E: like (A), a reef is growing
F: the left part of the volcano (Aitutaki's south end) is descending, but the right side remains
G: while the left/south part has completely submerged, the right part is still forming a mountain

Please note, that two of Aitutaki's motus have volcanic origin. The pictures are generalized.
In general, the reef is not forming a perfect, closed perimeter, but is often divided into smaller 'motus'.

Your Tasks

To log this Earth Cache, you have to fulfill two tasks. Both are physical, but in different meanings.

West coast trailhead onto the Mangua Pu	Reef on western side of Aitutaki, seen from the peak of MaungaPu

1. Visit the highest point of the island, the Maunga Pu. If you want please take a photo of you and your GPS receiver, so that the sourrounding area is recognizable, and feel free to post this picture with your online log
   Do not attempt to go there by driving a scooter!
2. Measure the overall, average tilting angle of the formation. I do not care about "the perfect number", but I want to see how you measured. Measure localy with some improvised water-level or plumb line, or in a wider area by using the altimeter of your GPSr at two different, representative locations. Or bring your pocket-theodolite. Be creative, but document your approach with a photo! Feel free to add a sketch of your "construction". If you are not afraid of someone "stealing" your approach, then also add these pictures to your online log.
   I highly appreciate weird concepts, as long as they are based on classic physics.
   Again, the focus is on the measuring arrangement, and not on the number or precision of results. The geological structure to be measured is only a small part of the massif.

Send me a short description of your measurement and the result via my user profile. Please do not log your visit without my permission.

Some Points of Interest

• The Peak of Maunga Pu, the highest place on Aitutaki (119m)
  S18 50.32166 W159 46.81633
• The western start of the path to the Maunga Pu (recommended starting point)
  S18 50.214 W159 46.93167
• A good place along the path to take a measurement
  S18 50.432 W159 46.808

Some Links of Interest

• Atoll on Wikipedia
• Aitutaki on Wikipedia

Update April 4th, 2011, according to GSA guidelines from Jan. 1st, 2011: no photo of yourself required to log online. Please add photos of your "measuring equippment".