Coastal Geology of Hawaii: Beaches, Reefs, Landslides

This website focuses on the coastal geology of Hawaii, and more specifically on the Beaches, Reefs, Landslides and Shoreline Features.

We need to start out by looking at the importance of the ocean to the islands of Hawaii.  Geologically the ocean is very important to Hawaii.  Its erosional powers shape the island’s wonderful landscapes and will eventually destroy these volcanic giants that grew from the sea.  In the place of these large masses will be living communities of coral and deposits of limestone

About the Designers

Billy

Emily

Thumbnails below are from: Thom Wilch, Tim Lincoln, Billy Howland and one from www.  For more details on www picture go to the Landslides page

Albion College geology students and professors created these web pages as a follow-up to our March 2003 Geology 210 Regional Field Geology class trip to Hawaii.  The images, except where noted, are a product of our trip.  We make them available for non-profit, educational uses.  As a condition of use, we request that you inform the page author or Thom Wilch.  Thank You.

Beaches

White and Cream Beaches (Waikiki on Oahu; Hapuna on Hawaii)

Composition: Mostly calcareous sand.Explanation:  The white sand beaches come from the breaking up of coral and other crustations, marine shell animals, etc.  Wave action will tear up pieces of these marine creatures, round them and deposits them onshore. Many times the larger pieces are broken in the larger storms that are associated with the winter month and hurricane season.

Black Beaches

  • Type #1: Glassy Volcanic Debris from littoral Explosions (Kalapana (Kaimu) and Punaluu on Hawaii).  Littoral explosions are those that are mixed with water and are very explosive especially for these usually tame basaltic eruptions.  These many times result in large deposits of ash with rock debris incorporated within it.
  • Type #2: Fragments of lava rocks (Waipio Valley on Hawaii).  These form in the same way as many classic beaches.  Wave erosion cuts into lava rocks and forms a beach.
  • Type #3: Magnetite and ilmenite eroded from lava rocks.  These are much like the green sand beaches in that they are composed mainly of minerals.  The difference is that these minerals are dark and not green.

Explanation: Black sand beaches of Hawaii come directly from the lava flows from the island.  Many times, these are short lived beaches because they originate from a single event and are then covered up by later lava flows.

Green Beaches ( Hanauma Bay, Oahu; 5 km NE of S. Point on Hawaii)

These are olivine beaches (Hanauma Bay’s olivine comes from tuff cones NE of Koko Head)Explanation: This most unusual of all of the beaches comes from lavas, cinders and tuffs that are rich in olivine.  Olivine is the first mineral to crystallize out of magma and is by far the most noticeable phenocryst in these Hawaiian basalts.

Many Hawaiian beaches contain some amount of white, black and green sand, which is easy to see if you take a close look at the sand at any beach you visit in Hawaii.

Albion College geology students and professors created these web pages as a follow-up to our March 2003 Geology 210 Regional Field Geology class trip to Hawaii.  The images, except where noted, are a product of our trip.  We make them available for non-profit, educational uses.  As a condition of use, we request that you inform the page author or Thom Wilch.  Thank You.

Reefs

Introduction: Snorkeling in Hawaii can give an up-close chance to really look at the coral and its inhabitants and understand life beneath the surface. But it is important to remember to keep the environment clean and not to disturb the living homes of many sea creatures. The top of Diamond Head crater is a fantastic place to view the reefs from afar.  We swam among the coral reef and tropical fish at Hanauma Bay (below).


Fringing Coral Reefs (Hanauma Bay on Oahu and the only type that we saw)

Composition: Living sea organisms and remains of sea organisms.

Explanation: Fringing coral reefs form in the warm, shallow sea water surrounding the Hawaiian Islands near shore. Marine organisms like the families Pocilloporidae and Poritidae  live in branching colonies in the warm water. They thrive in the light and build the colonies to reach just below the surface of the water. As they die, they continue to build on the skeletons of dead organisms, creating a massive reef zone. The coral can then become a habitat for other sea animals. Sea urchins and tropical fish live among the coral. Among the Hanauma Bay corals were Hawaiian Sergeants, Blackspot Sergeants, and Convict Tangs as well as abundant types of urchins.

Barrier Reefs

Composition: Living sea organisms and remains of sea organisms.

Explanation: Barrier reefs are located some distance away from shore and are separated by a lagoon.  In this intermediate stage subsidence and erosion are important.

Atolls

Composition: Living sea organisms and remains of sea organisms.

Explanation: These are later stage in reef formation.  They are roughly circular and have no central land mass.  In this stage the dominant feature is the lagoon in the center of the Atoll.  At this stage the volcanic rocks are no longer present at the sea surface.  These can be found to the northwest end of the Hawaiian Chain.


Landslides


Landforms

Tsunamis

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