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At the southern tip of the Maldives, on the tiny island of Villingili,part of the land rises up to 2.4 metres above the sea. It’s the world’s
lowest high point. With most islands just a metre or so above the sea
level, it is often suggested that the world’s lowest country may drownbeneath rising sea levels by the end of the century. For tourists, thisranks the Maldives at the top of lists of destinations to visit before they
disappear. For the 400,000 people who live on the islands, things arerather more serious: rising sea levels could make them climate change. Such scenarios of flood and drowning assume that the land
surface remains unchanged. But, what if the land could build up verticallyas sea levels rise? This is what colleagues and I have been examining in
our research, now published in Geophysical Research Letters. We studied
five reef islands in the southern Maldives and found that they wereactually built up when sea levels were higher than they are today.
The Maldives is a nation of around 1,200 coral reef islands. Reef
islands are unique landforms in that they are formed entirely of sediments
produced by corals and organisms that live on coral reefs in thesurrounding waters.

, this dependence on the coral reef for island-building sediments, combined with elevations rarely more than a few
metres above the sea, means that reef islands are often considered among
the environments most vulnerable to climate change, particularly to sea
level rise. This is of particular concern for nations such as the Maldivesthat are built entirely on reef islands, and whose citizens have nowhere
else to go.
To improve predictions of how reef islands may respond to futureenvironmental change, it is important to understand how they responded, we reconstructed the island-

to environmental change in the past.

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（Ea⑥）

building histories of five islands in the southern Maldives. We firstcollected 28 reef island sediment samples, or cores. This basically involved
hammering an aluminium pipe into the reef island until it reached theisland “foundations”

a point lower than the live coral in the surrounding

ocean. The cores enabled us to access the layers of sediment that havebuilt up throughout the island’s history. We then analysed these sediments
under the microscope to find out what exactly the island is made of. Inaddition, we radiocarbon dated the sediments to determine when thevarious layers were created.
Results showed that the key phase of reef island building occurred
between 4,200 and 1,600 years ago, when sea levels reached around 0.5
metres higher than they are today. In addition, this was probably
happening under the influence of large wave events caused by distant
storms. These waves would have had the power to break pieces of coral off
the reef.

, these pieces of coral, as well as sand from the reef, built

up to form the islands. Climate change will mean rising sea levels andeven stronger large wave events in the future. It may therefore recreate
conditions that are conducive to reef island building, which may enable
these islands to keep growing vertically. This would make the islands
more resilient and may even be necessary for them simply torising

sea levels. Our work complements other studies which are showing thatislands are in fact dynamic landforms that are able to move and adjust in
response to environmental change.
All this should make reef islands in the Maldives more physicallyresilient. However,can also make islands more difficult for humans

to live on, for instance by damaging houses and farmland, or by dumping
salt into supplies of fresh water. Reef island nations will have to develop
infrastructure that can resist, or be adaptable to, such powerful waves.
Such infrastructure must still allow natural processes to take place,

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however, so that reef islands can maintain active connections to theirsurrounding coral reefs.
While our study suggests that rising sea levels could benefit reefislands in some regards, they still remain at risk. For instance, we also
found the islands in our study were made mainly of coral

about 75%.

This means a healthy reef will be essential if the islands are to keep
growing in future, and the Maldives are to remain above the waves.
, coral reefs are threatened by climate change, not just by rising
sea levels, but also by warmer and more acidic oceans. Under climatechange, we may therefore end up in an odd situation where we have theperfectconditions

tobuild

coral

reef

islands,

butofbuilding

materials.
(Adapted from a work by Holly East)（注）．sediment

沈殿物，堆積物．elevation

隆起．vulnerable

被害をこうむりやすい．radiocarbon date

放射性炭素年代を測定する．be conducive to〜〜に貢献する，〜を促す．resilient

強い，回復力のある．complement

補足する．infrastructure（道路，ダム，堤防などの）基盤設備，インフラ．acidic

酸性の――

（Ea⑥）

〔〕本文の〜それぞれに入れるのに最も適当なものを ⑴ 〜 ⑷から一つ選び，その番号を解答欄にマークしなさい。

⑴

researchers⑵ supporters⑶

tourists⑷ victims⑴

After that

⑵ However⑶

Similarly⑷ To make matters worse⑴

Furthermore⑵ Needless to say⑶

On the other hand⑷ With this goal in mind⑴

A few years ago⑵ All of a sudden⑶

Over time⑷ Previously⑴

keep pace with⑵ make space for⑶prevent⑷ reflect⑴

constant growth⑵ coral reefs⑶

large waves⑷ such resilience⑴

And yet⑵ Fortunately⑶

Indeed⑷ Instead⑴

a collection⑵ a waste⑶an absence⑷ the existence――（Ea⑥）

〔〕下線部〜

それぞれの意味または内容として，最も適当なものを ⑴ 〜 ⑷から一つ選び，その番号を解答欄にマークしなさい。

this⑴the island rising up in the Maldives⑵

the Maldives being the world’s lowest country⑶

many islands in the Maldives being just a metre or so above thesea level⑷

the Maldives being likely to disappear under the sea by the endof the century

This⑴

The fact that climate change can negatively influence reef islands⑵

The fact that there are around 1,200 coral reef islands in theMaldives⑶

The fact that sediments produced by organisms make reef islands
more livable⑷

The fact that people living in nations like the Maldives have
nowhere else to go

Results⑴

Results from examining whether the Maldives are built entirely on
reef islands⑵

Results of predicting how reef islands may respond to futureenvironmental change⑶

Results from investigating the influence of large wave events onreef islands in the Maldives⑷

Resultsofreconstructing

theisland-building

historiesoffive

islands in the southern Maldives――（Ea⑥）

It⑴

The reef⑵

Climate change⑶

The islands’ history⑷

The key phase of reef island building

Our study⑴

The study of the declining tourism of the Maldives⑵

The study of how reef islands evolved in the Maldives⑶

The study of the impact of coral reefs in the Maldives on humans⑷

The study of materials which could be used to repair reefs in theMaldives――（Ea⑥）