Yamada Line

A railway between Morioka and the Sanriku coast had already been designated in the Railway Construction Act of 1892, originally as a route from Morioka to Rikuchū-Yamada. Surveys were carried out, but because the line had to cross the Kitakami Mountains between Morioka and Miyako — over the Kuzakai Pass, at 751 metres above sea level — the project failed to take concrete shape for decades. Construction was finally decided in 1920, after Hara Takashi, a native of Iwate Prefecture who had become Prime Minister of Japan two years earlier, threw his weight behind it. Building such a line through sparsely populated mountains was controversial; a much-repeated anecdote has an opposition member jeering that the government meant to "carry monkeys" over the pass, to which Hara is said to have replied that railway regulations did not provide for carrying monkeys.

The line opened in stages. The first section, from Morioka to Kami-Yonai (9.9 km), opened on 10 October 1923. It was then extended eastward step by step — reaching Kuzakai in 1928, Rikuchū-Kawai in 1933 and Miyako on 6 November 1934 — and on 17 November 1935 a further section carried it south along the coast from Miyako to Rikuchū-Yamada. The southward extension continued as part of a planned Sanriku trunk line defined in the Revised Railway Construction Act, reaching Iwate-Funakoshi and Ōtsuchi before the final section from Ōtsuchi to Kamaishi opened on 17 September 1939, completing the through route from Morioka to Kamaishi on the eve of the Pacific War.

After opening, trains between Morioka and Miyako were often so crowded that passengers had to stand. Until the Kamaishi Line was completed in 1950, the Yamada Line was the only direct rail connection between the coast and the interior of northern Iwate, and once it reached Kamaishi in 1939 it carried freight day and night, linking the steelworks and mines of Kamaishi with the Tōhoku Main Line. In November 1946 a severe storm and flood cut the line between Hiratsuto and Toyomane; full restoration took until 1954, and as a stop-gap the occupation authorities (GHQ) pressed for the Kamaishi Line to be rebuilt through to Kamaishi. Once that line opened, the main inland freight route shifted away from the Yamada Line and its relative importance declined. Steam locomotive (Class C58) operation ended on 28 February 1970, and freight service over the whole Morioka–Kamaishi line ceased on 1 November 1986.

With the privatisation of Japanese National Railways on 1 April 1987, the Yamada Line was succeeded by JR East and integrated into its network. New KiHa 100 series diesel cars entered service from 7 July 1991. Over the following decades several lightly used mountain stations were closed: the remote Ōshida and Asagishi stations, long among Japan's least-used "secret" stations, were skipped by all trains in winter from 2013 and abolished on 26 March 2016, and Hiratsuto Station was abolished on 17 March 2023, both owing to declining passenger numbers.

The Great East Japan Earthquake of 11 March 2011 devastated the coastal part of the line. Along the 55.4-kilometre Miyako–Kamaishi section, 21.7 kilometres were flooded and four of the section's thirteen stations, together with roughly a tenth of the track, six bridges and ten embankments, were destroyed; the stations at Origasa, Ōtsuchi and Unosumai were washed away and Rikuchū-Yamada burned down in a tsunami-driven fire. The inland Morioka–Miyako section reopened on 26 March 2011, but rail service on the coastal Miyako–Kamaishi section would not resume for eight years.

For the coastal section JR East twice proposed, in 2012 and again in 2013, converting the damaged right-of-way into a bus rapid transit (BRT) route, as had been done on the Kesennuma and Ōfunato lines; both times the four local municipalities, whose town planning assumed a rail rebuild, rejected the idea. In 2014 JR East agreed to bear the bulk of the roughly ¥21 billion restoration cost and to transfer the rebuilt section to the third-sector Sanriku Railway. The Miyako–Kamaishi section reopened on 23 March 2019 and was handed over to Sanriku Railway, which joined it with its former Kita-Rias and Minami-Rias lines into a single, continuous Rias Line. The Yamada Line thereafter consists only of the inland Morioka–Miyako section, which remains a JR East rural line and no longer reaches the town of Yamada from which it takes its name.

• 1892A railway from Morioka to Rikuchū-Yamada toward the Sanriku coast is designated in the Railway Construction Act, but the mountain crossing keeps it from being built for decades.
• 1920Construction is finally decided after Iwate-born Prime Minister Hara Takashi backs the line.
• 192310 October: the first section, Morioka–Kami-Yonai (9.9 km), opens.
• 192825 September: the line is extended from Kami-Yonai to Kuzakai (25.7 km).
• 19346 November: the Rikuchū-Kawai–Miyako section (28.6 km) opens, bringing the line to Miyako.
• 193517 November: the line is extended south along the coast from Miyako to Rikuchū-Yamada (26.5 km).
• 193917 September: the final section, Ōtsuchi–Kamaishi (12.3 km), opens, completing the through route from Morioka to Kamaishi.
• 194626 November: a storm and flood cut the Hiratsuto–Toyomane section; full restoration of the line is not completed until 1954.
• 197028 February: steam locomotive (Class C58) operation ends; the line is dieselised the next day.
• 19861 November: freight service over the whole Morioka–Kamaishi line is discontinued.
• 19871 April: with the privatisation of Japanese National Railways, the line is succeeded by JR East.
• 19917 July: KiHa 100 series diesel cars enter service on the line.
• 201111 March: the Great East Japan Earthquake floods 21.7 km of the 55.4 km Miyako–Kamaishi section and destroys four of its thirteen stations; the inland Morioka–Miyako section reopens on 26 March.
• 201626 March: the remote Ōshida and Asagishi stations, among Japan's least-used stations, are abolished.
• 201923 March: the Miyako–Kamaishi section reopens and is transferred to Sanriku Railway, becoming part of its Rias Line.
• 202318 March: Hiratsuto Station is abolished owing to declining passenger numbers.