The United States Geological Survey (USGS) said a magnitude 5.2 seismic event struck near the border between Nepal and China.
It added that a “glacial collapse and debris flow” caused “subsequent catastrophic impacts downstream”.
Rescue efforts had previously been hampered by fears of more flooding from a lake formed by the glacier collapse which sparked the flooding.
Dame Joanna said having visited and travelled in the country, “it breaks my heart because I know how difficult it is to get around”.
“It seems that we have been warned about this over the years,” she added.
“I do believe that what we do here, and the fossil fuels we burn and the plastic waste in the sea and so on, I do believe that is making the world a sicker place and a weaker place.
“And the places which are melting fastest are the high mountains and places, and so the Himalayas are there.”
Dame Joanna is the patron of healthcare charity Doctors for Nepal and vice patron of The Gurkha Welfare Trust, which provides aid to Gurkha veterans who served in the British Army.
Her father served in the 6th Gurkha Rifles, a regiment of the British Indian Army, during the Second World War.
Vice Lord-Lieutenant Colonel Jane Davis, former Coronation Street star Sally Lindsay, drummer Steve White and Greenwich mayor David Wardrop also joined the vigil.
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