Geography teachers are concerned that plans to abolish A-level coursework could put an end to vital fieldwork.
The Qualifications and Curriculum Authority has advised ministers to remove the coursework requirement in most A-levels.
But in a letter to Alan Johnson, the Education Secretary, John Hopkin, chair of the Geographical Association's education committee, said: "Because of the close connection between coursework and fieldwork, an end to the former will severely damage the latter.
"Without a requirement for coursework, and pressure from senior managers to save time and resources, fieldwork will effectively cease to be a requirement for all students."
Dr Hopkin told The TES: "Enquiry runs through geography like a stick of rock. Ours is not a subject where pupils are told about things. They find them out for themselves.
"It's about going out into the real world and investigating it. That's a very marketable skill for the world of work. But it's difficult to test enquiry skills in an examination."
Dr Hopkin fears that if the fieldwork requirement is removed from geography A-level, it will eventually disappear from geography GCSE as well.
"Some youngsters thrive on the investigative element of the course," he said. "If they're tested on a narrower range of skills, their attainment will suffer."
David Roberts, assistant headteacher and geography teacher at Middleton technology school, in Rochdale, said: "This is the thin end of the wedge.
"It is like saying, 'Yes, you can study science, but you can't do any experiments in a laboratory. Or, 'You can study English literature, but you can't read any books.' Geography is about what's out there. You can look at textbooks about glaciers, or use the internet and PowerPoint, but it's not the same as standing on a glacier."
Jon Samson, a geography teacher at Brooklands college, in Surrey, agrees.
He said he was already under pressure from senior management to justify the financial and health-and-safety risks involved in taking pupils on field-trips. Without the coursework requirement, he said, such trips would vanish entirely.
"One of the reasons learners like geography is because it gets them outside," he said.
"They can immerse themselves in the subject - really get a sense of what it's about. Students like the idea of doing things for themselves."
Teachers say these skills are vital if pupils want to study geography at university.
Antony Allchin, head of geography at Worthing college, in West Sussex, said: "At A-level, pupils want a subject they can get their teeth into - that enables them to do things on their own. That is an important stepping-stone to degree-level study. How can an examination assess research?"
The QCA has recommended dropping coursework from most A-level subjects as part of its overhaul of the 16-19 curriculum.
The move follows widespread concerns about plagiarism among pupils. But certain subjects - including art, music and dance - in which coursework is deemed to be integral to the curriculum, are exempt from the new proposals.
A spokesman for the QCA said: "We would not deny the importance of fieldwork to geography students. But we are trying to decrease the amount of prescription.
"We want schools to manage the process. You would imagine that in a two-year course they would spend at least some time doing real field studies."