= Solution
Using the preceding conductive estimate, warmer incoming crust is less dense. Interpret the given $\alpha=10^{-5}\,\mathrm{K^{-1}}$ as the volumetric coefficient entering $\delta\rho/\rho=-\alpha\Delta T$. The representative contrast gives
$$
\frac{|\delta\rho|}{\rho_s}=\alpha\Delta\overline T_c\simeq0.0035.
$$
For $\rho_s\simeq3000\,\mathrm{kg\,m^{-3}}$, that is only about $10.5\,\mathrm{kg\,m^{-3}}$. Let $L$ be the vertical thickness of the anomalous slab material in a compensated column. Its mass deficit per unit area is approximately $\rho_s\alpha\Delta\overline T_c L$. If uplift adds compensating column mass $\rho_{\rm ref}\Delta H$, isostatic balance gives the <thermal buoyancy support of topography>:
$$
\Delta H\simeq\frac{\rho_s}{\rho_{\rm ref}}\alpha\Delta\overline T_c L.
$$
The reference density depends on which interfaces move in the assumed column model. For approximately equal densities and a near-horizontal $7$ km crustal layer, this gives \b[$\Delta H\simeq25$ m]; using $\rho_s=3000$ and $\rho_{\rm ref}=3300\,\mathrm{kg\,m^{-3}}$ gives about \b[$22$ m]. A modest dip changes the vertical intersection to approximately $h_c/\cos\theta$ and does not change this order of magnitude. Different graphical flux choices and uncertain geometry change the number; they do not justify replacing a $7$ km crustal anomaly by a whole $100$ km lithospheric anomaly without additional information.
Thus \b[the crust-only thermal contrast can supply tens of metres of isostatic relief, not kilometres]. Its sign would favor greater thermal support from the warmer Juan de Fuca crust, so it cannot by itself explain why much of the central <Andes> stands higher than <Cascadia>. Crustal shortening and roots, whole-slab thermal structure, phase transformations, hydration, magmatic addition and dynamic stresses can dominate. If the stated expansion coefficient instead meant a linear solid expansion coefficient, the first-order density coefficient would be about three times larger; the estimate would still be well below kilometre-scale mountain relief.
To test <isostasy>, jointly measure <surface topography>, <free-air gravity anomalies>, <Bouguer gravity anomalies> and crustal thickness from <receiver functions> and <seismic refraction surveys>. An <Airy isostasy> interpretation predicts crustal roots beneath high terrain and a corresponding regional negative Bouguer signal; thermal or compositional compensation predicts different density structure. Compare gravity and <geoid> observations with compensated-column predictions over a range of wavelengths, and use <gravity-topography admittance> to test local versus <flexural isostasy>. A small long-wavelength free-air anomaly can support compensation, but is not a sufficient test by itself. <GNSS> uplift, leveling and dated marine or river terraces constrain transient or sustained vertical motion; <seismic tomography> and rock-density estimates constrain deeper buoyancy. Residual relief or gravity after these corrections may require <dynamic topography> or tectonic support. \b[An actively deforming subduction margin need not satisfy instantaneous local isostatic equilibrium], even if the estimate above is a useful scale comparison.
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