An elderly German couple who died in Trephina Gorge in Central Australia wandered up to 17 kilometres off a marked walk before dying of dehydration and heat stress, an inquest has found.

Key points: The Thors died of "environmental heat injury", an autopsy found

The Thors died of "environmental heat injury", an autopsy found A review found several issues, including missing fence and trail markings, inadequate safety messaging

A review found several issues, including missing fence and trail markings, inadequate safety messaging Their son recommended that people traveling to remote locations without mobile coverage should download a GPS application, as well as an offline map

Northern Territory coroner Greg Cavanagh released his findings into the deaths of Wilfred Thor, 75, and his wife Gisela, 73, on Monday.

The couple left their accommodation in Alice Springs at 6am on February 10, 2017, to travel to the East MacDonnell Ranges.

Their detailed itinerary described plans to visit Emily Gap and Jessie Gap, before travelling 100 kilometres east of Alice Springs to Trephina Gorge, where they had intended to complete a one-hour hike.

They were experienced travellers and hikers who had visited the United States, Canada, Namibia and South Africa in recent years.

"The deaths of my parents was a tragedy and for us, it is not to blame somebody, an institution or even a particular person," their son Matthias told the inquest.

"The only thing we can do is to learn from it and to do our best to avoid [so] those tragedies will never happen again."

Gisela and Wilfred Thor perished while walking at the Trephina Gorge near Alice Springs. ( Supplied: Thor family )

Trail obscured by grass, fence washed away

The temperatures in Berlin in February hovered around zero degrees Celsius, whereas February in Central Australia is extremely hot, with temperatures reaching almost 40 degrees Celsius, Mr Cavanagh's findings stated.

In his findings, which traced the Thors' final steps, Mr Cavanagh said they parked at the Trephina Gorge car park about 9.30am and set out on a two-kilometre walk; because it was so short they took only one 600 millilitre bottle of water.

However, 400 metres into the walk, the trail itself and an orange marker indicating the correct direction were obscured by long grass, so the Thors walked past it.

A wire stock fence that usually marked the boundary of the park, along with a laminated sign warning visitors not to go any further, had been washed away by flooding two weeks earlier.

The fence was due to be repaired only three days after the couple set off on their hike. ( ABC News: Nick Hose )

The Thors continued walking for a few kilometres until the terrain became impassable, at which point they turned back, refilling their water bottle from the creek bed.

Mrs Thor took a right turn and walked out of the creek bed 400 metres later, following a small sandy trail.

"Why she left the creek bed is not known," Mr Cavanagh said.

"However, it is likely that by that time it was very hot. The temperature for the day rose to 39.9 degrees Celsius. She was not wearing a hat and may well have been suffering heat stress and dehydration."

Couple separated, suffering heat stress

He said Mr Thor did not notice her go, as he was presumably walking ahead of her, and went another 700 metres before turning back.

"Mrs Thor… walked for another 900 metres before sitting down under the shade of a small tree," Mr Cavanagh said, noting that at that point she was only 20 metres from a graded track on the pastoral station.

"However, her footprints were not found on the edges of that track and it is probable that she was unaware of the track. She fell sideways. That was the position in which she was found, deceased."

From the point of leaving the car to that position she had walked about 10 kilometres.

Map The German couple are thought to have died on their first day at Trephina Gorge.

For his part, Mr Thor continued to walk along the tributary in an area where there was no water, walking up a small incline more than 3 kilometres later and sitting on a rock.

"He is likely also to have been suffering heat stress and dehydration by that time. He had walked 17 kilometres," Mr Cavanagh said.

"It is unlikely that Mr Thor understood his dire situation. He lay back on the rock. He was found deceased in that position."

Death of experienced walkers a tragedy, coroner says

The following day, two tourists noticed the Thors' car in the parking lot, and drove towards the ranger station, flagging down a ranger and telling them about the car.

But it was his day off, and he was heading to Alice Springs with his family.

"It would have been better if prior to [going to Alice Springs] he had investigated the vehicle and reported the matter; however it must be remembered that the walks were relatively short," Mr Cavanagh said.

The longer walk, the Ridgetop walk, was four to five hours each way, and sometimes people would walk it in cooler weather and camp overnight at the other end, returning the next day.

Mr Cavanagh also said that apart from one minor incident, there had been no previous issues with tourists becoming lost in the park.

There hadn't been any serious previous issues with tourists getting lost at the gorge. ( Wikimedia: Prince Roy )

The ranger went back to the Trephina Gorge car park later that afternoon, following the Thors' tracks before notifying police that night, but it took four days for authorities to discover Mr Thor. Mrs Thor was not found until the fifth day of the search.

"I note that the two missing persons have come from a German winter to a hot dry climate. They will not be acclimatised and therefore unable to dissipate heat effectively," a Dr Luckin told police at the time.

"I note the extreme daytime temperatures, warm, hot nights, low humidity, rocky terrain reflecting heat and lack of shelter. All of these will cause rapid dehydration, hyperthermia and collapse."

An autopsy ruled that the couple died of "environmental heat injury".

"The deaths of Mr and Mrs Thor were a tragedy. They were experienced walkers," Mr Cavanagh said.

"They were on a holiday that was extremely well planned and researched. The only available explanation is that their decision making became impaired by the heat and dehydration after walking out of the Park."

GPS apps recommended

After the deaths of the Thors, a Parks and Wildlife review found a number of issues; including the absence of the boundary fence, the adequacy of the signage and track marking, the adequacy of safety messaging available to visitors before visiting the park, the failure to immediately commence a search on initial notification and the lack of mobile or Wi-Fi coverage.

Gisela Thor's son urged people travelling to remote locations to download a GPS app to their phones. ( Supplied: Thor family )

"Those issues were considered and where within their power, acted upon," Mr Cavanagh said.

A new emergency response procedure was implemented, requiring all potential incidents to be reported immediately; and a "beat the heat" safety campaign was launched this month.

The Thors' son urged people travelling to remote locations without mobile coverage to download a GPS application to their phones ahead of their journey, as well as an offline map for their destination.

"People should just have the mobile phone with them, which is something most people will do anyway," he said.

"In the event of getting lost they should switch it on, start the GPS app, wait for the signal and just follow the arrow on the display to the road, carpark, or next human settlement."

Mr Cavanagh recommended that the Department of Tourism and Culture do whatever necessary to advise visitors in areas without phone reception of the existence of GPS applications.

"This tragedy illustrates that systems such as signage and fencing can fail; the purpose of having backup systems is that failure of one does not necessarily result in tragedy," he said.