erupt in smiles

１２日朝、JR広島駅の山陽線の電車の上に猫が乗り、１９分発車が遅れました。また、その様子などがTwitterに投稿されると、１５００件超ものリツイートがされました。

Cat atop train in Hiroshima delays departure -- and becomes Twitter sensation
HIROSHIMA -- A cat sitting atop a train at JR Hiroshima Station delayed its departure for 19 minutes, setting off a flurry of activity via Twitter while delighting passengers.

A photo of the feline calmly reclining atop the Sanyo Line train that was posted to Twitter was re-tweeted more than 1,500 times, along with comments such as "How can you get angry at this?" and "This is just such a peaceful scene. It made me feel really calm inside."

At around 8:35 a.m. on April 12, the train conductor alerted the station reporting, "We've got a cat here."

The kitty had perched itself atop the fourth car of an eight-car regular service train, which had set out from Shiraichi Station and was bound for Iwakuni Station in neighboring Yamaguchi Prefecture.

When train station employees ran over to where the cat was sitting, it hopped down onto the tracks in front of them and then jumped up on the platform before scampering away.

While this was occurring, an announcement was made inside the train, saying, "There is a cat on top of the train, and the driver is now checking out the situation." According to comments made on Twitter, "passengers inside the train erupted in smiles" as soon as the announcement was made.

A public relations representative with West Japan Railway Co.'s Hiroshima branch office commented, "I guess the cat didn't hear the message from the train station giving instructions to stay behind the white line."

"I'm glad that the cat and the passengers are all fine," the official added.

http://mainichi.jp/english/articles/20160414/p2a/00m/0na/012000c

今回注目する表現は、”erupt in smiles”です。”erupt”という動詞は、「〈火山が〉噴火する」という意味がよく知られています。この記事の中ではどうでしょうか。『ウィズダム英和辞典』（第３版、三省堂）には、第３義に「〚〜in[into] A〛〈人・地域が〉突然A（状態）になる」と載っていました。

Macmillandictionary.comには、“if a place erupts, there is suddenly a lot of noise as people start shouting, laughing, or fighting”と定義されていて、

The room erupted in laughter as Sally acted out the incident.

という例文が示されていました。”erupt”を用いることで、突然さと勢いを表現できるようです。

なので、今回の記事は、「『車両の屋根に猫がいるため、運転士が確認しています。』というアナウンスが流れたその瞬間、思いかげず乗客には笑みがこぼれた。」と解釈できます。

なお、記事の最初の"We've got a cat here."は「至急、至急。緊急事態発生です。」を意味する
We've got/have a situation here.という警察などの連絡での鉄板フレーズを思い起し、面白いと感じました。（Blue Sky）