Inland and Lake Lighthouses
Freshwater Hazards
The popular image of a lighthouse places it on a rocky headland facing an ocean, battered by salt spray and visible for twenty miles across open water. The reality of the world's lighthouse network includes hundreds of towers that have never been washed by salt water, that stand on flat shorelines of freshwater lakes, or at the mouths of rivers that empty into those lakes, or on shallow shelf reefs that in some cases lie hundreds of miles from any coast. These lights are no less essential to the shipping that relies on them — and, in some respects, the environments in which they stand are as hostile as any ocean coast.
The Great Lakes of North America form the largest system of freshwater lakes in the world, containing about twenty-one percent of the world's fresh surface water by volume. Superior, Michigan, Huron, Erie, and Ontario are connected by rivers, straits, and canals into a navigable inland sea stretching roughly a thousand miles from the western end of Lake Superior to the St Lawrence River. The shipping that moves through this system carries iron ore, coal, grain, and limestone in quantities that make it one of the most important inland waterways in the world. At the system's peak, in the late nineteenth and early twentieth centuries, more individual vessel movements were recorded in the Sault Ste Marie canal between Superior and Huron than in any canal in the world including the Suez.
The Great Lakes Lighthouse System
The United States established its first Great Lakes lighthouse at Buffalo, New York, on Lake Erie in 1818, two years before it established its first lighthouse on the West Coast. By the end of the nineteenth century, the US Lighthouse Board operated over four hundred lights on the Great Lakes, ranging from major harbour lights at Chicago, Detroit, Cleveland, and Duluth to minor channel lights and range markers deep in harbours and river mouths.
Split Rock lighthouse on the north shore of Lake Superior is among the best-known lake lighthouses. Built in 1910 on a sheer anorthosite cliff sixty metres above the lake surface, it was constructed in response to the loss of twenty-nine ships in a single November storm in 1905. The site was extraordinarily difficult to build on — all materials had to be lifted up the cliff face — and the resulting tower is architecturally distinctive: an octagonal yellow brick structure with a focal plane 38 metres above the cliff base and 168 metres above lake level. The light, a third-order bivalve Fresnel lens, showed a flashing character visible at 22 nautical miles. Split Rock was deactivated in 1969, largely because GPS alternatives were available, and is now a Minnesota state historic site with significant visitor numbers.
The Stannard Rock lighthouse, built between 1877 and 1882 on a shoal 24 miles off the Michigan shore in Lake Superior, is often described as the most remote lighthouse on the Great Lakes. The rock itself barely breaks the surface, and the lighthouse stands in water more than 100 feet deep at its base, built on granite cribwork sunk to the lake bed. Its builders, led by Lighthouse Board engineer Orlando Metcalfe Poe, worked with the same constraints as offshore ocean lighthouse builders: limited access windows, severe weather, and no usable foundation above water. The lighthouse remains active, still marked on the chart as a significant hazard.
Spectacle Reef, also on Lake Huron, presented similar challenges. The stone lighthouse built there between 1871 and 1874 under Poe's direction was the most expensive lighthouse project in the United States to that point, and was regarded at the time as a feat of engineering comparable to anything achieved in European offshore lighthouse construction. The tower is 34 metres tall, built of precisely cut limestone blocks without mortar in the lower courses, each block interlocked with its neighbours by iron bolts and dowels.
Lake Lights and Weather
Great Lakes weather in November is among the most dangerous freshwater sailing weather in the world. The temperature gradient between the still-warm lake water and the cold air masses moving south from Canada generates storms that develop more rapidly than equivalent ocean storms, because the fetch — the distance over which wind builds waves — is relatively short but the energy input is intense. The waves that result are shorter and steeper than ocean swells of equivalent height, creating violent motion on vessels that are designed for long ocean swells.
The lighthouses of the Great Lakes were built with this weather in mind. Stone and brick construction prevailed over wood at all but the smallest positions; the thickness of the tower walls at exposed sites like Spectacle Reef and Stannard Rock is comparable to ocean offshore towers of the same period. Winter ice presented an additional hazard not found in salt water: lake ice forms earlier and more extensively than sea ice at comparable latitudes because freshwater freezes at a higher temperature than seawater, and ice pressure against a lighthouse foundation is enormous.
Several Great Lakes lighthouses were built with reinforced bases specifically to resist ice loading. The ice breaker bases — sloped granite structures that deflect ice up and over the foundation rather than allowing it to push against a vertical wall — were a local engineering innovation that differed from the construction practice used at ocean offshore towers.
The Baltic and Other Inland Seas
The Baltic Sea occupies a position between ocean and true inland water. It is effectively a large brackish lake, connected to the North Sea through the narrow straits between Denmark and Sweden, with a surface salinity much lower than the open ocean because the input from large freshwater rivers exceeds the exchange with salt water through the straits. Its lighthouse network has the characteristics of both inland and ocean lighthouse systems: significant freshwater rivers empty into it, requiring river entrance lights of the kind found on lake systems, while the open Baltic presents navigational challenges similar to coastal ocean navigation.
The Kõpu lighthouse in Estonia, built between 1505 and 1531, is among the oldest continuously operating lighthouses in the world. Standing 26 metres tall on the Hiiumaa peninsula at the entrance to the Gulf of Finland, it guided ships making their way through the Baltic to and from the ports of Tallinn, Riga, and St Petersburg. Its construction predates the systematic development of lighthouse technology; it was built as a beacon tower and has been modified repeatedly over five centuries to accommodate successive generations of lighting equipment.
Bengtskär lighthouse, in the outer archipelago southwest of the Finnish coast, represents a different tradition: a granite rock lighthouse built in 1906 at the entrance to the complex island-studded approach to the Finnish ports. Standing 52 metres tall on a wave-swept skerry, it was the scene of a significant military engagement during the Winter War in 1941, when Soviet naval forces attempted to land on the rock and were repulsed by Finnish troops. The lighthouse, still active, is now accessible to visitors by ferry from Hanko in summer.
River and Canal Lights
At the inland margins of the lighthouse system, river and canal entrance lights mark the transitions between open water and the confined channels where deep-draft vessels must navigate with great precision. These are often small structures — a pile-mounted lamp, a coloured post, a range light pair — rather than the architectural towers of the exposed coasts, but their function is identical: to tell the navigator exactly where the safe water is.
The lights at the mouths of the rivers entering the Great Lakes — the St Marys, the St Clair, the Detroit — guided the great ore carriers that constituted the bulk of the lake traffic. The combination of river current, changing depths, and the density of commercial traffic made these approaches genuinely demanding to navigate, and the aids to navigation were dense and precisely maintained.
The full distribution of lake and inland sea lighthouses, from the Great Lakes through the Baltic to the inland seas of Russia and the lakes of Africa, is recorded on Open the map, where the geographic spread of freshwater and brackish-water lighthouse towers illustrates how extensively the inland shipping networks of the world were equipped with the same navigational infrastructure as the ocean coasts.