The Maldives:

Sea-levels,Tsunamis and Coastal change

Sue Dawson&

Niklas Mörner

Islands are no more than 1.5 m above sea level

The MaldivesThe Maldives

Satellite photo of theAtolls making up the Maldives

Welcome to the Maldives

Some1200islands

Groupedin some 20largeratolls

“Queen’s Bath” (Hithadoo Island, Addoo Atoll)

(4) Shore terrace 400–800 BP: +60 cm

(5) High-tide level 1790–1970: +20-30 cm

(6) High-tide level today

(1) Mean-tide level today

A sea level fall ~1970-1975

-lowering of the erosion level-building out of lower shoreplane-owergrowing of old surface-weathering of old surface

The lowering was in the order of 20-30 cm

(probably an effect of increased evaporation, decreased precipita-tion and/or changed monsoonal regime)

The Maldives, 2002

Example of records of short high sea levels.

This coral, today 5-10 cm above mean zero,

and “in situ” requites a water depth of ~60

cm (according to Laborel), implying a

higher sea level of about +70 cm.

The coral is cut and dated at 2 levels.

(2) = 1585 +35 BP

(1) = 1635 +35 BP

Goidhoo Atoll

Fen cores

Sea level oscillations in the last millennium (cores from two fens)The 2 swamps became lakes in ~1790 and both dried up in ~1970

NB. Peat and shell dates differ by 350 years, a good measure of the local “sea correction”

The new sea level curve of the Maldives (Mörner, 2007) recording a number of oscillations driven by the redistribution of ocean water masses. The base line seems to peak at around 1300 BP (excluding any Mid-Holocene maximum as predicted by the loading models).

The combined observational records (in mm/year) for the last 300 years.It shows variations – ups and downs – but no trend.

For year 2100, INQUA gives predictions in line with this record,whilst the IPCC scenarios lie far above – way off – observational data

The ”flooding scenario” of IPCC does not concur with observational sea level facts. Therefore, it must be called-off as a mistake.

Today, we favour a 2100 value of +5 cm +15 cm

The MaldivesThe Maldives

EarthquakeEarthquakeEpicentreEpicentre2500 km2500 km3 hrs travel 3 hrs travel timetime

Satellite image 2 hrs after the earthquake

Tide data for Male and Gan

• Population: 290,000• Total number of islands

1,192• Number of inhabited

islands:199

Flooding Status• Only 9 islands had no

flooding• 69 islands completely

flooded

The MaldivesThe Maldives

Sand deposits across the airport

Gan, Laamu Atoll: Maldivestsunami sediment thickness 30cm

Finer sediment than the beach

Particle Size Analysis

Well sorted beach sands differFrom the overlying tsunami deposits

Isdhoo, Laamu Atoll, 2cm tsunami sediment And PSA profiles

Sediment plumesSediment plumes

Sediment plumes across the islands: protectionof the land from the reefs located up to 1km

offshore

Clear sediment plumes into the lagoon

Sediment plumes through to the lagoon inside the atoll (distance c. 500m.)

Coral debris plumes in the lee of trees and vegetation

Erosion scarp on the leeward side of the islands

Tsunami depositsOverlie the beach sands

Male

Highly built up- MaleWas severely flooded

Sea level oscillations in the last millennium (cores from two fens)The 2 swamps became lakes in ~1790 and both dried up in ~1970

NB. Peat and shell dates differ by 350 years, a good measure of the local “sea correction”

Ostracod and Foraminifera

Elphidium sp.

Quinqueloculina

Quadracythere sp.

Spiroloculina

Laamu Atoll

Potential for chronologyof extreme events

Table 1. Submarine shedding of sand into caves with radiocarbon dating of shells and coral after subtraction of 350 years for regional “sea correction”.

Tsunami in AD 1733: (1) in fen records (left), (2) in submarine caves (right) and (3) in a historical record of ”a disastrous flooding in 1733.

The Lisbon earthquake–Tsunami is classical

and similar events are bound to re-occur in the near-future

When a coastal segment experiences erosion, a ”sea level rise” is often advocated.The reality is much more complicated:

in fact, a sea level lowering generally causes more erosion!The clue is often what actually is to be found on the lee-side