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Geology of the Hawaiian IslandsGeology of the Hawaiian IslandsClass 24Class 24

8 April 20048 April 2004

Any Questions?Any Questions? Rise and fall of sea level and Rise and fall of sea level and its effect on Hawai`iits effect on Hawai`i

Sea levelSea level

Has fluctuated up and down many Has fluctuated up and down many times in the geologic pasttimes in the geologic pastEvidence?Evidence?

Wave attack causes the land to be eroded back, leaving a wave-cut terrace

WaveWave--cut terraces cut terraces

Formed only at sea level, and Formed only at sea level, and therefore indicate former sea level therefore indicate former sea level Coral reefsCoral reefs

Old reefs can be found both above and Old reefs can be found both above and below present sea levelbelow present sea level

Sea Level ChangeSea Level ChangeSea level has fluctuated greatly over the Sea level has fluctuated greatly over the past 900,000 yearspast 900,000 yearsGlaciers hold large amounts of waterGlaciers hold large amounts of waterWhen they melt, the water goes into the When they melt, the water goes into the ocean and sea level risesocean and sea level risesWhen they expand, they pull water in from When they expand, they pull water in from the oceans and global sea level dropsthe oceans and global sea level drops

Drowned shorelinesmark former sea levels

Modern

Ancient

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Sea Level ChangeSea Level ChangeAbout 15,000 years ago, much of the About 15,000 years ago, much of the earth's surface was covered by glaciers earth's surface was covered by glaciers and sea level was about 120m lower and sea level was about 120m lower than it is todaythan it is today

Sea Level ChangeSea Level ChangeIn past 15,000 yrs, the glaciers have In past 15,000 yrs, the glaciers have been retreating and meltingbeen retreating and meltingGlobal sea level has risen to where it is Global sea level has risen to where it is todaytoday

Sea Level ChangeSea Level Change25% of Hawaii's natural, endemic 25% of Hawaii's natural, endemic vegetation grows along the coastal vegetation grows along the coastal zone zone Shorelines around the world, including Shorelines around the world, including those in Hawaii, are undergoing longthose in Hawaii, are undergoing long--term retreat due to rising sea levelterm retreat due to rising sea level

Hawaiian tide gages Hawaiian tide gages document a history document a history of local seaof local sea--level level

riserise

Sea Level is rising Sea Level is rising around the world at around the world at

1.5 to 2.2 1.5 to 2.2 cm/decadecm/decade

SLR is projected to SLR is projected to accelerate over the accelerate over the

next centurynext centurySeaSea--level rise forces shoreline retreat and erosionlevel rise forces shoreline retreat and erosion

Beach erosion vs. Coastal erosionBeach erosion vs. Coastal erosionCoastal erosion occurs when coastal area Coastal erosion occurs when coastal area moves inland due to rising sea levelsmoves inland due to rising sea levelsDuring coastal erosion the beaches move along During coastal erosion the beaches move along with the rest of the system and the beaches are with the rest of the system and the beaches are not erodednot eroded

Beach equilibriumBeach equilibriumEffect of Sea Level rise depends on slope of Effect of Sea Level rise depends on slope of beachbeach

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Beach equilibriumBeach equilibriumBeaches respond to storms by Beaches respond to storms by retreating landward, either flattening retreating landward, either flattening their profile, or forming offshore barstheir profile, or forming offshore barsThe effect is to dissipate wave energy The effect is to dissipate wave energy over a broad zone and thus reduce over a broad zone and thus reduce shoreline retreatshoreline retreat

Studies show a Studies show a 150x erosion 150x erosion

multiplier where multiplier where sea level rises sea level rises along sandy along sandy shorelines. shorelines.

Hence, for a Hence, for a mean 0.24 m rise mean 0.24 m rise by 2050, beaches by 2050, beaches will recede 36 m will recede 36 m

(118 ft)(118 ft)

Chronic coastal erosion is a statewide problemChronic coastal erosion is a statewide problem

FEMA FEMA National National coastal coastal erosion erosion study of study of 60 year 60 year erosion erosion hazard, hazard, 19961996

Seawalls are constructed where there is erosion, but they do not solve the erosion – they often worsen it along adjacent shores because they block sand.

Hawaii needs erosion solutions.

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Water quality suffers on armored shoresWater quality suffers on armored shoresHigh turbulence from wave reflectionHigh turbulence from wave reflection

Fleshy algal growthFleshy algal growthLittoral ecosystem heavily damaged Littoral ecosystem heavily damaged

Erosion is caused by Erosion is caused by 1. Sea1. Sea--level rise forcing shoreline retreat level rise forcing shoreline retreat 2. Waves and currents moving sand2. Waves and currents moving sand3. Human impacts to sand availability3. Human impacts to sand availability

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Beach Loss Beach Loss Due to Human InterferenceDue to Human Interference

One One --fourth of Oahu fourth of Oahu beaches are lost due beaches are lost due to armoringto armoringOneOne--third of Maui third of Maui beaches are lost due beaches are lost due to armoringto armoringBeaches are 50Beaches are 50--70% 70% narrower in front of narrower in front of wallswalls

Coastal access is Coastal access is decreaseddecreasedLittoral ecosystem is Littoral ecosystem is damageddamagedCoastal dunes are Coastal dunes are destroyeddestroyedCultural practices Cultural practices impactedimpactedTourism economy Tourism economy impactedimpacted

Human ImpactsHuman Impacts

1. Sand impoundment1. Sand impoundment

2. Longshore trapping 2. Longshore trapping

3. End scour 3. End scour

4. Drainage channel4. Drainage channeldredgingdredging

5. Dune leveling/filling5. Dune leveling/filling

6. Sand mining6. Sand mining

Poor SandPoor SandManagementManagement

Sand mining Sand mining at Waimea at Waimea Bay caused Bay caused over 200 ft over 200 ft of erosionof erosion

COUNTY CONTROLCOUNTY CONTROL

Setbacks do not offer Setbacks do not offer adequate protectionadequate protection

Large lots are Large lots are subdivided, density is subdivided, density is rising on all shoresrising on all shores

Zoning ordinances fail Zoning ordinances fail to discriminate erosion to discriminate erosion

hazardshazards

Armoring has Armoring has been a been a

universal tool universal tool in Hawaiiin Hawaii

…but new …but new tools are tools are

moving to the moving to the forefrontforefront

NEW POLICY DIRECTIONS

Avoid development of eroding lands

Discourage additional development in erosion hazard

zones

Acquire high value coastal lands

Construction guidelines for hazard areas

Nourish eroding shores

Beach Beach RestorationRestoration

by sand by sand nourishment nourishment is a worldis a world--wide tool in wide tool in managing managing

coastal coastal erosion.erosion.

Erosion ControlErosion ControlWaikiki Waikiki –– KuhioKuhio BeachBeach

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DEMONSTRATIONDEMONSTRATION

State Program State Program General Permit General Permit

SmallSmall--Scale Beach Scale Beach Nourishment Nourishment

StreamlinesStreamlinespermitting forpermitting for

10,000 yd10,000 yd33 sand sand replenishment replenishment

projectsprojects

Demonstration Demonstration project showed project showed minimal impactminimal impact

No turbidity No turbidity

Stable beach Stable beach configurationconfiguration

(30(30--100 yds100 yds33/ft)/ft)

Community Community acceptance acceptance

(20 ft increase)(20 ft increase) Sand fields are found adjacent to most Sand fields are found adjacent to most Hawaiian shorelinesHawaiian shorelines

Can offshore sand be sustainably mined with Can offshore sand be sustainably mined with minimal environmental impact?minimal environmental impact?

Unfortunately, the Unfortunately, the largest and most largest and most immediate source immediate source

of beach sand of beach sand often lies under often lies under our homes and our homes and

roads roads –– this sand this sand is released by is released by erosion of the erosion of the

coastlinecoastline

Beach LossBeach Loss

Do we protect nearDo we protect near--shore property shore property and lose the beaches?and lose the beaches?Or protect the beaches and lose Or protect the beaches and lose the property? the property?

Questions? Questions?

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Coral ReefsCoral ReefsConstructed from calcareous Constructed from calcareous

remains and secretions of remains and secretions of corals and calcareous algaecorals and calcareous algae

Coral reefs are often called the Coral reefs are often called the “Rainforests of the Sea”“Rainforests of the Sea”

About 4,000 species of fish and 800 About 4,000 species of fish and 800 species of reefspecies of reef--building coral have been building coral have been identifiedidentified

Coral reefs are a vital protein Coral reefs are a vital protein source for many ...source for many ...

Globally, oneGlobally, one--fifth of all animal protein fifth of all animal protein consumed by humans comes from marine consumed by humans comes from marine environmentsenvironmentsCoral reefs provideCoral reefs providefood for one billionfood for one billionpeople in Asia alonepeople in Asia alone

Coral reefsCoral reefs

Mostly confined to warm, clear Mostly confined to warm, clear waters of the tropical Pacific and waters of the tropical Pacific and Indian OceansIndian OceansAlso found in Caribbean and Also found in Caribbean and Mediterranean SeasMediterranean Seas

Global distribution of coral reefsGlobal distribution of coral reefs

A significant part of a coral reef is formed of skeletons of small animals and plants inside a branching frame-work built by the corals

Limey secretions of algae bind the entire structure together

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Coral reefsCoral reefs

Grow best in waters with Grow best in waters with aveave. annual . annual temperature of 24temperature of 24°°C (75C (75°°F)F)Can’t survive sudden temp changes or Can’t survive sudden temp changes or prolonged exposure to temp less than prolonged exposure to temp less than 18 18 °°C C Require clear, sunlit waterRequire clear, sunlit waterLimiting depth of reef growth is about Limiting depth of reef growth is about 45 meters45 meters

Reef exposed at low tide

Reefs grow upward and outward

Erosion

Talus

Reefs also grow inward

Darwin’s AtollTheory

Drilling into Pacificatolls found basalt in the lagoons, confirm-ing the theory.

Some of the Some of the MaldiveMaldive

Islands in Islands in the Pacificthe Pacific

Atoll

Fringing Reef

Guido Alberto Rosi/The Image Bank

Barrier Reef Surrounding Volcanic IslandBarrier Reef Surrounding Volcanic Island

Lagoon

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Hawaii’s ReefsHawaii’s ReefsRepresent 85% of all reefs in U.S.Represent 85% of all reefs in U.S.More than 25% of species found on More than 25% of species found on Hawaiian reefs not found anywhere Hawaiian reefs not found anywhere else in the worldelse in the world

Reefs are fragile systems Reefs are fragile systems that are now endangeredthat are now endangered

The The Reefs at RiskReefs at Risk IndicatorIndicator

LowLow MediumMedium HighHigh

Results are sobering ...Results are sobering ...

Nearly 60% of the world’s reefs were Nearly 60% of the world’s reefs were found to be at risk from human activitiesfound to be at risk from human activitiesReefs with the highest levels of Reefs with the highest levels of biodiversity are threatened biodiversity are threatened Most U.S. reefs are at riskMost U.S. reefs are at risk

Many things can hurt reefsMany things can hurt reefsWavesWavesStarfishStarfishPeoplePeople

Seasonal wave energy on all shores

Occasional highenergy events on all shores (storms)

There are very few reefs now growing around Hawai`i because of the nearly constant wavesThere are many old reefs around There are many old reefs around Hawai`i Hawai`i –– Have the weather Have the weather patterns changed??patterns changed??

Many things can hurt reefsMany things can hurt reefsWavesWavesStarfishStarfish

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Many things can hurt reefsMany things can hurt reefs

WavesWavesStarfishStarfishCrownCrown--ofof--ThornsThorns

Many things can hurt reefsMany things can hurt reefs

CrownCrown--ofof--ThornsThornsA single CrownA single Crown--ofof--Thorns eats Thorns eats 5m5m22

per year of coralper year of coral

People create problems for ReefsPeople create problems for Reefs

People like to collect pretty reef fishPeople like to collect pretty reef fishPeople import foreign species which take People import foreign species which take over the reefover the reefDredging and dumping hurts reefsDredging and dumping hurts reefsRunoff can contain chemicalsRunoff can contain chemicalsBoat anchors kill coralBoat anchors kill coral

Coastal development ...Coastal development ...

Dredging Dredging Construction Construction materialsmaterialsBuilding on Building on reefsreefsNutrients from Nutrients from sewage sewage Sediments Sediments Unregulated Unregulated tourismtourism

Tourists can love reefs to deathTourists can love reefs to death Destructive fishing practices in Destructive fishing practices in Southeast Asia are widespreadSoutheast Asia are widespread

Areas atHigh Risk

Rivers transport inland pollution Rivers transport inland pollution directly to reefsdirectly to reefs

Soil sediments Soil sediments resulting from resulting from deforestationdeforestationInappropriate Inappropriate agricultural agricultural practicespractices

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Questions? Questions? TuesdayTuesday

GlaciationGlaciation and Global Climate Changeand Global Climate ChangeRead Chapter 11Read Chapter 11