How Did We Map the Sea Floor in the Past?
The first survey to map the sea floor in the United States was completed in 1834 on the south shore of Long Island, New York.
It was done using lead lines and sounding poles.
Lead lines were ropes with numbers marked along them, like a ruler. A lead weight was attached at the end.
Sounding poles are like big rulers.
Surveyors used these tools for a long time. A surveyor lowered a line into the ocean. When it hit the bottom, he marked the measurement and pulled it up. He wrote down measurements from different parts of the ocean. Then he put them on a chart to create a “picture” of the ocean floor. The measurements were often right, but the uncharted spaces between them were really big. Many objects were missed. Some were rocks as big as your house! These objects caused many shipwrecks.
Modern tools let us see all of the sea floor.