The mega fauna mass extinction during the Pleistocene was a time of quickly rising sea levels, mega fires, mega dust storms , mega flooding and mega lahars. You can see video on line of Lahars that happened when the snow pack on Mt Saint Helen’s instantly melted at the time of the eruption and left hundreds of miles of destruction along what had been river canals and along the banks. Closer to the mountain lahars created all new geological topography in the flash of the instant when they occurred. The danger of lahars in the glaciated mountains is apparent in the Northwest on many of the major volcano’s. Lahar action can be found world wide. The great melt down of the Continental ice glaciers from the last ice age came in phases over a period of 5000 years and the lahars that could be produced could be 1000s of times more powerful than anything observed on the slopes of Mt Saint Helen’s. That means that instantly a volume of water 1000 times greater than comes out of the mouth of the Amazon river or the Columbia river could instantly find it self scouring the continental landscape and also scouring the bottom of the ocean as it flowed down though parts of the continental shelf that were submerged during the ice age. Some continental shelf canyons which seem to be an underwater mystery today can be explained in part as the product of areas prone to huge ice melt off stream lehar action when sea levels were up to 400 lower. Mega fauna was much at risk because of the ice melt down because they tended to live on lower continental elevations near sources of water that included larger rivers and lakes. Those areas were at great risk of being hit by melt down. The large mega fauna creates might have lived part time on top of the glaciers but food sources did not tend to grow on top of the ice and with the climate being cooler during the ice age partly because of the reflectivity of the ice covering so much more of earth ‘surface it means higher elevations were more prone to be ice covered especially in the northern and souther hemispheres as opposed to close to the equator. Mega fauna was not likely a high elevation type of habitat enjoying class of animals but an at risk low lying class. Mega fauna was at risk of the 400 ft of coastal flooding experienced over the 5000 year period of on and off melt down that occurred. One thing to remember is that high elevations were cold just as now and the warmest north and south hemispheric areas would have been areas closest to the oceans at as much 400 ft below present day sea levels. The best forests and grass lands would have been below 5000 ft elevation just the way they tend to be today.
The rich bio diverse coastal planes were at high risk of Lahar action going many miles inland putting mega fauna at risk from multiple life threatening events of catastrophic Lahar destruction. Examples of the worst of the lahars are places like the Columbia River Gorge where whole mountains were swept away by catastrophic flooding possibly emanating from a ice dam breaking or even an asteroid stile of the highlands ice pack. Lahars would have swept away top soil and left wasteland worse than had it just been a flood that occurred. Lahar action could totally transform the landscape to unrecognizable levels. Just watch a video of the Mt Saint Helen’s eruption lahars and think of that as being possible to 1000 times the magnitude of destruction The great ice age meltdown was a really lousy time to be an extra large mega fauna animal because Lahar after Lahar occurred disturbing all your habitat as sea levels were also rising to destroy that too. between the flooding and the sea level rise drowning coastal areas , mega fauna was always at risk of the forces of the Lahar too. imagine the glaciers melting with waterfalls that could span miles and be as much as 8000 ft high channeling melt waters from the glaciers. The lahars would seek the path of least Resistance most of the time keeping them in existing river Chanel’s but that could not stop lahars from creating brand new paths of least Resistance across all parts of the continental landscape.