Scientists studying the recent eruption at White Island say people on the crater floor may have been killed if the hot ash surge happened during daylight hours.

The eruption, which left the crater floor covered in green ash, was a ‘hot volcanic surge deposit'.

An inside view of White Island's crate lake. Photo: Supplied

It travelled horizontally across the crater floor, and didn't fall from the sky as often occurs. It has a texture like ‘apple crumble' and was very dry, indicating it was very hot when deposited.

'Survivability during the eruption would have been low on much of the crater floor,” says volcanologist Brad Scott.

The green colour is the result of a unique combination of minerals on White Island.

'The ash contained quite a bit of pale yellow sulphur which appeared as irregular shaped lumps, and some translucent golden yellow grains. This is consistent with the colour of the deposit.

'The eruption deposit at the North rim site was typical of what volcanologists refer to as a hot volcanic surge deposit. It was plastered on sides facing the vent, but was absent on shaded/protected surfaces.”

The eruption happened about 9.20pm on Wednesday, April 27.

On Thursday morning, scientists were able to see from the island webcam the indications of a new deposit.

Later in the morning, they also noted that two of the solar panels didn't start to charge batteries, suggesting they were covered in ash.

'We knew something had happened but it wasn't until GNS volcanologists flew over the volcano in the afternoon they were able to fully appreciate the impacts of the previous night's eruption,” says Brad.

The dark yellow-green ash deposit from the eruption covered about 80 per cent of the floor of the Main Crater, blasted high up the sides of the crater wall on both the north and south sides.

At a distance of 500 m from the eruption site the ash deposit is about 5 mm thick. It extended off the island to the north east.

From the photography and thermal images taken on Friday afternoon scientists were able to identify the location of a new vent that had erupted on Wednesday evening.

Significant collapse also occurred in this area, formally known as Donald Duck Crater. Several meters of Donald Mound have collapsed into the 1978/90 Crater area.

Analysis of the ash found no new material. New material is an indication of the start of a new phase of activity. The eruption only tossed out old lake sediments and crater wall material.

'From our past experience of examining White Island ash we are confident that this is not April 2016, magma,” says Brad.