Geology of the Hawaiian Islands Class 24 8 April 2004 Any Questions? Rise and fall of sea level and its effect on Hawai`i Sea level Has fluctuated up and down many times in the geologic past Evidence? 1
Wave attack causes the land to be eroded back, leaving a wave-cut terrace Wave-cut terraces Formed only at sea level, and therefore indicate former sea level Coral reefs Old reefs can be found both above and below present sea level Sea Level Change Sea level has fluctuated greatly over the past 900,000 years Glaciers hold large amounts of water When they melt, the water goes into the ocean and sea level rises When they expand, they pull water in from the oceans and global sea level drops Modern Drowned shorelines mark former sea levels Ancient 2
Sea Level Change About 15,000 years ago, much of the earth's surface was covered by glaciers and sea level was about 120m lower than it is today Sea Level Change In past 15,000 yrs, the glaciers have been retreating and melting Global sea level has risen to where it is today 3
Sea Level Change 25% of Hawaii's natural, endemic vegetation grows along the coastal zone Shorelines around the world, including those in Hawaii, are undergoing long- term retreat due to rising sea level Hawaiian tide gages document a history of local sea-level rise Sea Level is rising around the world at 1.5 to 2.2 cm/decade SLR is projected to accelerate over the next century Beach erosion vs. Coastal erosion Coastal erosion occurs when coastal area moves inland due to rising sea levels During coastal erosion the beaches move along with the rest of the system and the beaches are not eroded Sea-level rise forces shoreline retreat and erosion 4
Beach equilibrium Effect of Sea Level rise depends on slope of beach Beach equilibrium Beaches respond to storms by retreating landward, either flattening their profile, or forming offshore bars The effect is to dissipate wave energy over a broad zone and thus reduce shoreline retreat Studies show a 150x erosion multiplier where sea level rises along sandy shorelines. Hence, for a mean 0.24 m rise by 2050, beaches will recede 36 m (118 ft) 5
FEMA National coastal erosion study of 60 year erosion hazard, 1996 Chronic coastal erosion is a statewide problem 6
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. Water quality suffers on armored shores High turbulence from wave reflection Fleshy algal growth Littoral ecosystem heavily damaged 7
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Erosion is caused by 1. Sea-level rise forcing shoreline retreat 2. Waves and currents moving sand 3. Human impacts to sand availability 9
Beach Loss Due to Human Interference One -fourth of Oahu Coastal access is beaches are lost due decreased to armoring Littoral ecosystem is damaged One-third of Maui Coastal dunes are beaches are lost due destroyed to armoring Cultural practices Beaches are 50-70% impacted narrower in front of Tourism economy walls impacted Human Impacts 1. Sand impoundment 2. Longshore trapping 3. End scour 4. Drainage channel dredging 5. Dune leveling/filling 6. Sand mining Poor Sand Management COUNTY CONTROL Sand mining at Waimea Bay caused over 200 ft of erosion Setbacks do not offer adequate protection Large lots are subdivided, density is rising on all shores Zoning ordinances fail to discriminate erosion hazards 10
Armoring has been a universal tool in Hawaii but new tools are moving to the forefront 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 Restoration by sand nourishment is a world- wide tool in managing coastal erosion. Erosion Control Waikiki Kuhio Beach 11
DEMONSTRATION State Program General Permit Small-Scale Scale Beach Nourishment Streamlines permitting for 10,000 yd 3 sand replenishment projects Demonstration project showed minimal impact No turbidity Stable beach configuration (30-100 yds 3 /ft) Community acceptance (20 ft increase) Sand fields are found adjacent to most Hawaiian shorelines 12
Can offshore sand be sustainably mined with minimal environmental impact? Unfortunately, the largest and most immediate source of beach sand often lies under our homes and roads this sand is released by erosion of the coastline Beach Loss Do we protect near-shore property and lose the beaches? Or protect the beaches and lose the property? 13
Questions? Coral Reefs Constructed from calcareous remains and secretions of corals and calcareous algae Coral reefs are often called the Rainforests of the Sea About 4,000 species of fish and 800 species of reef-building coral have been identified 14
Coral reefs are a vital protein source for many... Globally, one-fifth of all animal protein consumed by humans comes from marine environments Coral reefs provide food for one billion people in Asia alone Coral reefs Mostly confined to warm, clear waters of the tropical Pacific and Indian Oceans Also found in Caribbean and Mediterranean Seas Global distribution of coral reefs 15
A significant part of a coral reef is formed of skeletons of small animals and plants inside a branching framework built by the corals Limey secretions of algae bind the entire structure together Coral reefs Grow best in waters with ave.. annual temperature of 24 C C (75 F) Can t survive sudden temp changes or prolonged exposure to temp less than 18 C Require clear, sunlit water Limiting depth of reef growth is about 45 meters 16
Reef exposed at low tide Erosion Talus Reefs grow upward and outward 17
Reefs also grow inward Darwin s Atoll Theory Drilling into Pacific atolls found basalt in the lagoons, confirming the theory. Atoll Fringing Reef Some of the Maldive Islands in the Pacific Lagoon Barrier Reef Surrounding Volcanic Island Guido Alberto Rosi/The Image Bank 18
Hawaii s Reefs Represent 85% of all reefs in U.S. More than 25% of species found on Hawaiian reefs not found anywhere else in the world Reefs are fragile systems that are now endangered The Reefs at Risk Indicator Results are sobering... Nearly 60% of the world s reefs were found to be at risk from human activities Reefs with the highest levels of biodiversity are threatened Most U.S. reefs are at risk Low Medium High 19
Many things can hurt reefs Waves Starfish People Seasonal wave energy on all shores Occasional high energy events on all shores (storms) There are very few reefs now growing around Hawai`i because of the nearly constant waves There are many old reefs around Hawai`i Have the weather patterns changed?? Many things can hurt reefs Waves Starfish 20
Many things can hurt reefs Waves Starfish Crown-of of-thorns Many things can hurt reefs Crown-of of-thorns A single Crown-of of-thorns eats 5m 2 per year of coral 21
People create problems for Reefs People like to collect pretty reef fish People import foreign species which take over the reef Dredging and dumping hurts reefs Runoff can contain chemicals Boat anchors kill coral Coastal development... Tourists can love reefs to death Dredging Construction materials Building on reefs Nutrients from sewage Sediments Unregulated tourism 22
Destructive fishing practices in Southeast Asia are widespread Areas at High Risk Rivers transport inland pollution directly to reefs Soil sediments resulting from deforestation Inappropriate agricultural practices Questions? Tuesday Glaciation and Global Climate Change Read Chapter 11 23