Indonesia's geological agency raised Merapi's alert level, which had been at the third-highest level since it began erupting last year.
More than 20,000 people in eight villages within 6 to 12 kilometers (4 to 7 miles) of Kanlaon would have to be evacuated if the volcano shows signs of an imminent eruption.
Authorities said they were closely monitoring the volcano which is located on an uninhabited island in the Sunda Strait.
Mount Merapi's last major eruption in 2010 killed more than 300 people and forced the evacuation of 280,000 residents.
Wallenda started his 550 meter walk across the crater known as 'The Mouth of Hell' at 8:20 pm Wednesday and finished 31 minutes later, sweaty and cheerful.
Juno has logged nearly 235 million kilometers since entering Jupiter's orbit on July 4, 2016.
Cancelled flights, missed connections and expiring visas have turned Bali into a nightmare for thousands of tourists scrambling to leave as volcano erupts.
The Mount Agung volcano on Bali has erupted for the first time in more than half a century, forcing closure of the Indonesian tourist island's busy airport as the mountain gushes huge columns of ash.
More than 40,000 people have been evacuated over fears of an imminent volcanic eruption at Mount Agung on Bali, is the world's most volcanic area.
A rumbling volcano on the resort island of Bali could erupt at any moment, authorities warned as they raised alert levels to maximum.
Huge plumes of smoke have been pouring out of the volcano since Tuesday and official said it was belching thick grey smoke.
A volcano on the Indonesian tourist island of Bali sent plumes of grey smoke and steam thousands of metres into the air for the third day in a week.
Mount Agung belched smoke as high as 700 metres (2,300 feet) above its summit late yesterday afternoon, sparking an exodus from the settlements near the mountain.
Indonesia, where nearly 50,000 people have been evacuated over fears of an imminent volcanic eruption at Mount Agung on Bali, is the world's most volcanic region with 129 active volcanoes.
Mount Agung, 75 kilometres (47 miles) from the tourist hub of Kuta, has been shaking since August and threatening to erupt for the first time in more than 50 years.