What early 1900s development using sound waves made mapping the topography of the ocean floor...

Explanation:
Although underwater listening devices had been used by Leonardo da Vinci in the late 15th century, underwater detection using echo ranging was initially developed (likely) as a response to the Titanic disaster in 1912. Initially intended for the detection of icebergs by 1914 it was used to map the ocean bottom off the Grand Banks.