Shown above are three images from the landslides in 1955. The damage occurred very close to multiple buildings and appears extensive.

Looking between these two images, there are several changes in the treeline, including one just east of Hillside Terrace. Given the time of year and looking at when other landslides in the area occurred, it is possible that there was a small landslide sometime between August and September of 1972.

So, what happened on Riverside Ave?

For decades, Riverside Ave has had the unfortunate pleasure of dealing with landslides. The main issues which have caused these landslides are the placement of fill along a steep slope combined with water. The removal of trees later on was an additional contributor. Going back to the 1872 topographic map, a large stream valley is visible on the south side of Riverside Ave. This is an important detail to pay attention to, because more water will travel into the stream valley and impact the steep slope on the north side of Riverside Ave.

In the early 1930s, the first placement of fill along Riverside Ave was recorded. At this point in time, there are trees on both sides of the road, but the road itself sits on top of fill which does not appear to be as stable as it should be. Moving forward to fall of 1955, three landslides were recorded in the span of several months and caused extensive damage. All of these occurred in areas where fill had been placed back in the 30s. It was likely that heavy rains triggered the already unstable slope repeatedly until the ground was too saturated and the material slid down the steep slope.

In 1962, aerial imagery shows a huge removal of trees within the stream valley. While this did not have immediate consequences, there were not as many trees in the area to absorb rainwater and groundwater. This resulted in more water moving downslope, north of Riverside Ave, to an area that had been filled. Several years later in 1968, another landslide occurred just northwest of the area where the trees had been cleared. It is important to note that this was the same area where the 2019 landslide occurred. Although there did not appear to be as much damage as the 1955 landslides, it raised enough concern that the state looked into preventing future landslides. Shortly afterwards between August and September of 1972, a small landslide potentially occurred in a similar area. Looking at aerial imagery, there is a slight difference in the tree canopy which is a possible indicator of a landslide.

In late summer of 1976, a landslide carried approximately 4000 cubic yards into the Winooski River. The material is visible protruding in the Winooski in the 1981 imagery. It was not visible in the 1974 imagery, indicating that it resulted from the 1976 landslide.

The last major landslide that occurred before the Halloween slide in 2019 took place in 1981 as a result of filling. A private landowner illegally dumped fill on his property, causing a landslide of trees, dirt, and debris along with further erosion of the slope. This event really opened the eyes of the city and state, who finally took action in 1983 to repair the area for good, or so they thought. Clay was removed from the slope and replaced with sand and rock. The new slope that was created was not as steep as the previous one either in order to reduce the hazardous risk.

Finally, on October 31st of 2019, a landslide triggered by heavy rains occurred in the same spot as the one in 1968. A second landslide occurring in the same spot suggests that that area is unstable to begin with. An already unstable area is more vulnerable, which is what happened in this case.

It has been almost 100 years since filling began on Riverside Ave, and while there have been large gaps in the timeline, Riverside Ave is still experiencing the same issues today as it has been over the century.