Welcome to Margaret River Mainbreak, WA’s premier surf location.
Before coming to Margaret River I had pictured the area as a large open river mouth that somehow created great waves. Upon actually seeing Margaret River I could see this wasn’t actually the case the river itself is actually a little underwhelming, the surf undeniably ‘cool’.
So what is behind this legendary location?
Margaret River is a well-known big wave location that constantly produces quality surfable waves between 0.6m – 7.6m all year-round. Swell travelling across the Indian Ocean from South Africa, raises up from deep water into a large A frame peak that peels left and right across the limestone reef. The ‘right-hander’ offers a steep wall and occasional tube that finishes on exposed reef. The ‘left-hander’ is longer, steeper and has a more intense tube that breaks across a dangerous shallow ledge (of reef) named Surgeons Table which has sadly claimed several lives.
The Leeuwin Current is the world’s longest known continuous coastal current and plays a dominant role in controlling the marine life and climate of Western Australia. Originating near Exmouth, it is a slender surface current less than 100km wide that transports warm, tropical water in varying strengths southwards down the WA coast before curling eastward around Cape Leeuwin and across the Great Australian Bight all the way to Tasmania!
The Leeuwin Current system consists of three major currents which exhibits seasonal and inter-annual variability: the warm southward flowing Leeuwin Current at the surface; the cool northward flowing Leeuwin undercurrent at 300-800m below the subsurface; and, the wind driven, cooler northward flowing Costal Current inshore of the continental shelf during the summer months.
The Leeuwin Current is stronger during winter and under La Nina conditions and weaker during summer and El Nino condition. In late spring the Leeuwin Current moves a little offshore and, with the onset of strong southerly winds is replaced by the costal Capes and Ningaloo Currents which die away in March/April. The costal currents promote mild upwellings of colder water at various unpredictable locations along the coast, most commonly measured near Rottnest Island and Cape Mentelle.
The Reef at Margaret River Mainbreak consists of Tamala Limestone. Tamala Limestone is the geological name given to the widely occurring eolianite limestone deposits on the western coastline of Western Australia, between Shark Bay in the north and nearly to Albany in the south. The rock consists of calcarenite wind-blown shell fragments and quartz sand which accumulated as coastal sand dunes during the middle and late Pleistocene and early Holocene eras. As a result of a process of sedimentation and water percolating through the shelly sands, the mixture later lithified when the lime content dissolved to cement the grains together. At this location the Reef is apart of the Rottnest Shelf. The Rottnest Shelf is a combination of shoreline platforms and offshore reefs formed by marine planation (levelling out of land surfaces by erosion).
To log this Earth Cache we require you to visit both waypoints, consider the information given and then message us with the following answers to the best of your ability.
- Looking towards the surf, estimate the height of the waves.
- What Geological feature is causing them to break.
- Head over to the second Waypoint and answer Q1 & 2 again noting any differences and what you think might be causing them.
- A photo of you or something significant to you/your team with the Margaret River surf in the background.
You are welcome to log your find straight away to keep your TB's and Stats in order but please message us with your answers within 24 hours. Cachers who do not fulfil the Earth Cache requirement will have their logs deleted.
Source: Geology.com, Wikipedia, Amrshire.wa.gov.au