In Finnish mythology, Vellamo is the siren-like goddess of the sea -- controlling storms and waves, wearing a dress made of foam, and caring for magical cows in underwater fields. Vellamo is also the name of the Finnish folk-pop duo performing a free show at the Menlo Park Library on March 20. And what it may lack in supernatural ocean cattle, the modern-day Vellamo makes up for in enchanting melodies, winsome vocals and a mix of original and traditional songs, sung in three languages.

"The reason we chose the name was that it comes from our folklore, sounds phonetically beautiful and is a badass goddess, which we consider pretty cool," lead singer Pia Leinonen said. She grew up in arctic Lapland (Finland's northernmost region), which she described as a land of extremes, with constant sunlight in summer and three months of darkness in winter.

The land of the midnight sun, northern lights and Santa Claus, is "very beautiful, but at the same time ruthless and harsh. It gives you perspective and a unique starting point for sure," she said. "There is a special relationship I have with 'the north' but it feels good to know that when I go back it is only for a visit. Permanently, I think the extremes would be too exhausting to me."

She and guitarist Joni Tiala are now based in Tiala's hometown, Kokkola, on Finland's western coast. The two met at a bar in 2008 and formed a partnership that's proven fruitful both musically and personally.

"One thing led to another and we fell in love with each other. We played music together from the very beginning," said Tiala. With help from some fellow folk-musician friends in Vermont, Vellamo's self-titled debut was released in 2013, followed by "Trad" in 2014 and "Koskenkylä" in 2015. "Trad" is a collection of Finnish and Swedish folk songs, while the other two albums are made up of both original compositions and traditionals and have drawn comparisons to bands such as Britain's Fairport Convention.

Leinonen is responsible for most of Vellamo's songwriting, while Tiala helps with arrangements.

"Writing the lyrics is my task," Leinonen said. "I have a piece of melody in my mind, sometimes with a couple of words, and that is where I start building the song."

"I know what chords would go along with the melody I have in mind. I can either find them myself, if they are within my limited selection of chords I know how to play with the guitar, or if they are not I'll just ask Joni to try out different chords until I hear the one I want."

Leinonen is able to sing in Finnish, English and Swedish. Finnish, naturally, comes first. "Because of the vowel/consonant ratio and pronunciation, it is a fun language to sing in," she said of her native tongue. When writing in her second fluent language, English, her lyrics tend to be more simple and descriptive, sung with a slight accent.

Leinonen learned to speak Swedish while at theater school.

"I love the Swedish language for its beautiful, soft, almost bouncy feel -- things that I don't associate with Finnish," she said.

Switching between the three languages is easy for Leinonen, only becoming tricky when addressing an audience of both Swedish and English speakers.

"Then I sometimes mix the languages and speak Swedish to the English speakers and vice versa," she said. "With Finnish there is no risk for that. As a language it is so different from anything else, really."

One of her English songs, "Letters to Sweet Zoey Li," from Vellamo's most recent record, describes a sad tale inspired by the ruins of a Chinese mineworker settlement she visited in New Zealand.

"The story behind that place was heartbreaking and did not leave me alone so I decided I'd have to write a song about it," she said. The song begins quietly but builds in intensity, with ethereal vocals contrasting with roaring guitar, giving the track a haunting, epic vibe.

"Colours of the Meadow," also from the newest album, is catchy bubblegum pop, with funky guitar and bass. Others, such as "Hey Little Bird," are pure folk in style, with intricate acoustic strumming and a timeless quality.

When choosing traditional folk songs, she looks first to the lyrics.

"If they feel like words I could sing, then we'll try playing it," she said. "Mannakorven mailla," for example, from their second record, is an old moonshining song (yes, she said, Finland also had a Prohibition era).

"In live situations we always play a rowdy, fun, uptempo, shout-along version of it but for the album we recorded more of a smoky and mysterious version," she said.

Back home, they sometimes play with a bassist and drummer, with Tiala on electric guitar, but on their tours of Europe, the U.S. and New Zealand they often play as an acoustic duo. In Finland, they also perform a puppet show for toddlers, drawing on Leinonen's theater training.

"She acts with these big hand puppets and I play music on a guitar throughout the whole 30-minute show. It is so much fun," Tiala said. He's a member of the progressive rock band Moonwagon, too, and, although he said guitar is his first love, the self-taught Tiala also plays keyboard, mandolin, bouzouki, dulcimer and ukulele, to name a few other instruments.

Menlo Park is the final stop on their current U.S. tour, which has included many concerts in public libraries.

"We love library shows. Those are listening-room types of shows and that is where our music really works at its best," rather than in noisy bars or clubs, Tiala said.

The group is currently completely independent, without a record label or booking agent to assist them.

"It feels really good to have all the freedom, but it's also hard work. It's very DIY. Basically it's just tons of emails and sitting at a computer endless amount of hours," he said. "It's getting a little bit easier every year, slowly making more and more contacts."

For tours across the U.S., they rent a campervan and drive themselves, sleeping in the van and staying at friends' houses when possible. Tiala said he enjoys seeing the changing landscapes on their travels.

"No matter where we go, people are very friendly and willing to help," he said.

With its distinctive blend of folk, rock and pop influences not to mention the multilingual repertoire -- Vellamo's sound stands out from the mainstream, and that suits the indie-music lovebirds just fine.

According to Tiala, "There is a pop music scene in Finland, but our kind of music doesn't really fit into that category so we are kind of outsiders, which I actually like!"

What: Vellamo

When: Sunday, March 20, at noon

Where: Menlo Park Library, 800 Alma St., Menlo Park

Cost: Free

Info: Go to Menlo Park Library and Vellamo.