Atoll Formation and Structure

• Atolls defined by coral reef rim totally/partially surrounding shallow central lagoon
• Located in tropical Indian and Pacific oceans
• Darwin's theory (1836): Reefs form around volcano islands, volcano erodes leaving reef and lagoon
  • Theory remains in textbooks but doesn't explain most atolls
• Modern theory: Sea level fluctuations expose flat-topped carbonate structures (volcanic/non-volcanic origin)
  • Rain pools in middle, dissolves limestone rocks via Karst process over ~100,000 years
  • Creates bowl-shaped rims
  • Sea levels rise again, submerging structure
  • Rocky rims become platforms for new corals

Atoll Island Formation

• Waves deposit loosely-held sediment onto shores until above water line
• Sediment sources (mostly biological):
  • Coral reef skeletal remains and broken pieces
  • Organisms grinding rock/coral (sea urchins, parrotfish)
  • Parrotfish generate up to 90% of reef sand in some areas
• Results in long, narrow strips of low-lying land
• Plants essential for soil creation and root systems prevent erosion

Sea Level Rise Threat

• Atoll islands extremely low-lying (sand can't pile higher than average wave height)
• Generally ≤3 meters above sea level, 5 max
• Maldives: 80% of 1,190 islands just 1 meter above sea level
• Global sea level rise past 130 years: 200mm total average
• 20th century: Tide gauge records
• Since 1993: Satellite measurements show acceleration to 3.3mm/year
• Central/west Pacific areas rising faster than global average

Evidence Against Island Submersion

• 2010 Marshall Islands study (Murray Ford):
  • 1946-2010: Sea levels rose 2.2-3.7mm/year
  • Over 80% of shorelines (vegetation line) grew larger or unchanged
• 2017 Maldives study (Mohamed Aslam):
  • 184 islands compared 1969 vs present
  • Net land area increased 59 hectares (2.4%)
  • 77 islands eroded, 36 added mass, 71 stable
• 2019 Atoll Island Database (Virginie Duvat):
  • 709 islands in Indian/Pacific oceans
  • 73.1% same size, 15.5% grew, 11.4% decreased
  • Smallest islands most volatile
• 2024 study (Paul Kench):
  • 509 islands over 50 years
  • 46.1% stable, 32.4% expanded, 21.4% contracted
• 2021 Chagos study (Mingyue Wu):
  • 36 years aerial photos of uninhabited Peros Banhos atoll
  • Net land size virtually unchanged 1979-2015 despite 5.4-5.9mm/year sea level rise

Island Dynamics

• Islands not static - created by coral sediment/sand deposited by waves
• Rising sea levels create higher, stronger waves depositing more sediment
• Island growth often faster than erosion
• Large swells/storms can erode or deposit sand depending on individual dynamics
• Shorelines highly variable - one side growing, other shrinking
• Islands can "migrate" - literally shift or rotate direction

Coral Reef Risks

• Coral reefs critical for sediment/sand production
• Bleaching events eliminate sediment source
• Causes: warming/acidifying oceans, algae blooms, coastal dredging, heat waves
• Overfishing and sewage affect animal life
• Parrotfish role in sand production underrated/important

Flooding and Storm Impacts

• Current rise: 3.2-4.2mm/year
• 2100 projections: 0.26-0.97 meters higher (or worse)
• Higher waves from cyclones and random swells
• Current swells: up to 5 meters high
• 2100 projection: Highest one-third of swells 5-10% higher in South Pacific
• 2007 Maldives example: 4-day tidal swells evacuated 1,649 people, damaged houses/schools, ruined crops
• King Tides rise over 3 meters, flood homes
• Cyclones can force population abandonment but also deposit sand creating new land

Freshwater Risks

• Freshwater from thin convex-shaped lens underneath island
• Recharged by rain, separate from saltwater
• Floods breach lens, raise salinity, make undrinkable
• Saltwater plumes persist months/years after floods
• Multiple floods can permanently impair lens

Flood Prevention Measures

• Natives historically lived with flooding/moving islands
• 1890s missionary record: "part of life and nobody minds"
• Natural processes work for unsettled islands
• Modern urbanized life not suited for annual floods
• Seawalls: Most common erosion prevention (cement bags, coral, steel, boulders, 0.5-1m tall)
  • Aesthetically ugly, disrupt sand accumulation
  • Taku atoll, Papua New Guinea: 1970s seawalls reduced beach width from 10m to 3m
  • Similar cases in Kiribati

Land Reclamation and Raising

• Maldives statistics: 93.5% of 188 inhabited/resort islands experienced shoreline modification
• Malé expansion: 33% growth (0.5 km²) since 1970s
• Hulhumale project:
  • Late 1990s: Malé expansion no longer possible due to depth
  • New island created by dredging sand onto coral reef
  • Phase I (1997): 5 years, $32 million, first residents 2004
  • Phase II (2015): Further expansion and infrastructure
  • 2018: Bridge connecting Hulhumale and Malé
  • Phase III (September 2023): Reclaim 63 hectares for housing crisis
  • Built 1.8m above sea level with sheet metal walls (north, west, south)
  • No serious floods yet, seawalls/dikes available if needed

Conclusion and Concerns

• Land reclamation criticized for exacerbating sea level rise impacts
• Sand dredging damages coral reefs, eliminates natural sand generation
• Maldives prefers "hard engineering" solutions
• 2004 Indonesian tsunami: Armored Malé protected vs unprotected outer islands
• Risk of sole dependence on engineering solutions
• Future concerns: Running out of money, resources, or sand for engineering options