This is an easy earthcache about the geology involved in lagoons and mudflats.
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- Based on the characteristics listed in this earthcache, look at the lake side at GZ. What characteristics are present that allow you to know that this lake was a lagoon with mudflats?
- Go to waypoint 1 (WP1). Look at the ocean side of the causeway and the pebble-lined shore. If you didn’t already know, what evidence do you see to confirm that this is a tidal bay?
- Other than civic planning, why would this location be a perfect place to build the causeway?
- [REQUIRED] Post a photo of yourself or a personal item at the site to prove you were there.
Bridge over Lost Lagoon, 1894
Here in Vancouver is Lost Lagoon in Stanley Park. However, despite its name, Lost Lagoon is not currently a lagoon, but is now a lake. The lake was created in 1916 by the construction of the Stanley Park causeway; until then, Lost Lagoon was a shallow part of Coal Harbour, which itself is an extension of Burrard Inlet.
Entrance to the park, with beginning construction of causeway, 1940
Lost Lagoon used to only appear during high tide. When the tide was in, water lapped the shores of the West End. When the water retreated with the tide, the lagoon disappeared entirely into mudflats.
Aerial view of Lost Lagoon, 1919
This area of mud flats was called Ch’elxwá7elch by the Squamish People, meaning "gets dry at times". The English name for Lost Lagoon comes from a poem written by Pauline Johnson, who named it due to the low tides leaving the harbour devoid of any water, causing her to lose her favorite canoeing and idling place for many days.
General characteristics of coastal lagoons:
Coastal lagoons form in shallow basins along gently sloping coasts where the sea level is rising relative to the land. They are usually separated from the ocean by a reef, island, or sand bank. The size and depth of coastal lagoons are often dependent on sea level.
Mudflats:
Mudflats form when silt and mud are brought in by seas, oceans, and tributaries. The mud and the silt are deposited into bays and lagoons when the tide comes in. The water mixes with the mud and silt, creating the muddy quicksand that occurs in mudflats.
A mud flat is defined as the upper zone of tidal flats where depositional processes are dominated by the fallout of suspended sediment, including sortable silts, flocs, and aggregates. It is characterized by intense bioturbation and the presence of various biogenic structures.
Mudflats are created by the deposition of fine silts and clays in sheltered low energy coastal environments such as estuaries, where they may form the largest part of the intertidal area. Mudflats play an important role in coastal defence, dissipating wave energy. Mudflats occur in sheltered bays and estuaries where water flow is slow enough for fine sediments carried by the tide and rivers to be deposited in layers of thick, sticky mud.
REFERENCES:
The History of Lost Lagoon
Stanley Park - Lost Lagoon walk | City of Vancouver
Mudflats - Buglife
Mudflats - Oceans, Coasts & Seashores (U.S. National Park Service)
Mud Flat - an overview | ScienceDirect
Lost Lagoon - Wikipedia