Gypsum Lakes or Birridas of Shark Bay

The Shark Bay or Birridas of Shark Bay is having outstanding natural features and a world Heritage site, the most westerly point of the Australian continent, next to the Indian. Scattered around Shark Bay, especially within Peron Peninsula inside the Francois Peron National Park, are a number of saline lakes of gypsum, famous among local’s peoples is “Birridas”.

It is believed thousands of years ago, when the sea levels were much higher than they are today, birridas were landlocked saline lakes among sand dunes. The water was so rich in sulphate of lime that was deposited onto the lake floor. But with the passage of time when the sea level dropped, the lakes dried up gradually and creating salty hollows and the sulphate of lime evaporated and became loose, powdery gypsum. The shape of Birridas is circular or oval and range from 100 m to 1 kilometer wide. They normally comprise of a central, raised platform ringed by a moat-like depression. The central section corresponds to the level of the water table during the late Pleistocene Period, about 10 000 years ago. Today, during very high winter tides or after heavy rains, when the groundwater level is raised, these moats fill with water to a shallow level.

Most birridas retain water for more than a few months following rain, and at those times, dormant eggs hatch and the birridas teem with brine shrimp, horse-shoe crabs and other invertebrates. They deliver a feast for wading birds such as red-necked stints and bar-tailed godwits that have migrated to Shark Bay from as far away as Siberia. Various birridas are connected to the sea by channels and receive seawater as well, where they form shallow bays. These bays are extremely imperative for fish breeding and nursery areas, although most birridas at Shark Bay are isolated, but are common in Francois Peron National Park where there are over 100 on the east coast of the Peron Peninsula. You can see birridas when driving around the park, however to appreciate the shapes and sheer number of birridas it is paramount to take a flight.

Source: Amusing Planet